Friday, January 23, 2009

My father, Ted Linden, 1938 - 2009

My father, Theodore Linden, died on Tuesday, January 20, 2009, a few months after being diagnosed with brain cancer.

My father valued reason and rationality above all else, which made particularly cruel the cancer that pulled his mind from him in pieces. During his lifetime, that mind had remarkable influence, including seminal work in computer security and object-oriented programming, helping to build the earliest graphical operating systems at Xerox, and designing early AIs for robotic vehicles.

The eyes of a child are not a mirror for the life of a father, but my earliest memories of my father's work is in the computer terminal he brought home with him from Xerox PARC. We would dial in to the mainframe using a funky acoustic modem, the kind where you would pick up a phone handset and plop it down into little soft cups so the computer could talk with little beeps into the phone. The reason I loved that terminal as a young child is that Dad would occasionally let me use it to play Haunt, an early, clever, and amusing game set in a haunted house that, to this day, remains my favorite text adventure of all time.

Later, he took me into Xerox and let me try a Xerox Star. I still remember the enormous removable hard drives, shaped like the saucer section of the Star Trek Enterprise, nearly a meter across. A child being a child, the main thing that sticks in my mind again was the games, such as Maze War, Draw, Trek, and Pinball. Those early experiences made me want to write computer games myself and eventually pushed me into computer science. History may not repeat, but it echoes, and I look on curiously as I see my own son starting down this same path.

The window through which a child sees is small. As an adult, I can more fully see the impact my father had. The Xerox Star and Alto were the foundation for all modern operating systems. The desktop metaphor, the mouse, all that we see on our computers in our daily lives today was built on the shoulders of research at Xerox. My father's work at Xerox (ACM) was a part of that on which others now stand.

After Xerox, in the early 1980's, he worked on the DARPA Autonomous Land Vehicle project (IEEE), an early attempt to build a car that drove itself. His research included replanning when the robot encountered unexpected conditions ([1]), work that much later would influence the planning systems used in the Mars Rover (IEEE). The ALV was too ambitious of a project to succeed with the technology available in the 1980's, but, in 2005, he looked on with pride and joy at the remarkable success of the nearby Stanford team when their car drove itself 150 miles down twisty desert roads in the DARPA Grand Challenge.

Even as an adult, I did not know about all my father did until recently. He lived his life with a quiet competence -- things just got done -- and never bragged or boasted. I was surprised, for example, to discover that he did seminal work in computer security (ACM) and object-oriented programming (ACM) way back in the 1970's. All of this from a man who was the son of a millwright, only in America.

My father spent much of his life in the study of intelligent systems. His children follow his footsteps. My sister has devoted her life's work to neurobiology and the study of the mind at University College London. I work in artificial intelligence and machine learning. As we look back at my father and a life well lived, we can only hope we might have a fraction of the positive impact he did. Ted Linden will be remembered and sorely missed.

If you knew my father or his work, please comment on this post. I would much enjoy hearing from you.

Update: Thank you, all of you, who posted comments on this post. I appreciate your thoughts and stories about my father.

Update: Two months later, on March 21, 2009, we held my father's memorial. It was our celebration and remembrance of his life. Below is my speech on that day:
In his retirement, in the wee hours of the morning, it was not unusual to find my father out of bed, downstairs, playing Civilization in his office. Basking in the gentle glow of his computer screen, he would relive the never-ending struggles of men and nations against each other, the competition for wealth, power, and influence we see throughout history.

Earlier, when I was at college, we both started looking at game theory. As part of my work, I built little simulations of people interacting that showed that, even when people have short-term incentives to hurt each other, they often cooperate. My Dad saw this and started devouring texts on the topic, looking at game theory, evolutionary economics, the incentives created by societies, and the emergence of cooperation. In all of this, he was seeking to understand how normally competing actors suddenly could start working together.

Throughout his life, my father was fascinated with the goodness of man. Why are people good to each other? Is it somehow innate? Can it be derived from reason? Is it part of the rules that successful societies build? How is it that altruism can exist?

Perhaps it was born of his Jesuit upbringing, looking to reason to explain the nature of man. It lived on in his career in computers and early artificial intelligence. He built robotic cars that attempted to learn about and navigate through the world. He studied how little programs running on different computers, without really trusting the other programs to do the right thing, could share knowledge to protect each other from outside threats. In his career, much of his work involved trying to build robots and agents that understand the world and cooperate with each other.

In all of it, he was motivated by the same questions: Why are people good? Why do people cooperate? In this world, how can altruism exist?

Like so many before him, my father only gained partial answers these questions. He saw rational people as able to see the benefits of cooperation in the long-term. He noted the societies we build reward cooperation and penalize cheating. He read of the benefits of altruism that accrue not only to ourselves, but to our families and societies. And he wondered if this was enough to explain the kindness we see around us.

Looking back as a son, I am inspired by my father's pursuit of such great questions. A life inquiring about the very essence of human nature, that is a life well lived.


Anonymous said...

My condolences. Your father sounds like an amazing guy. I never met him, but just from your description, I'm sad that he's not with us.

Here's to a life well spent!

Adam C. said...

Thanks for writing about him. While your loss is great, he will be remembered.

Daniel Tunkelang said...

Greg, I'm sorry about your loss. I lost my dad to Alzheimer's last year, and I see much my experience in your post.

Your dad managed to achieve the best kind of immortality, leaving enough inspiration behind to shared with future generations. That is an example for us all.

adinel said...

I'm deeply sorry about your loss. I was just reading his study when the news stoke the cloud. We lost a great man. Thanks for sharing with us.
Here is a version on Security and Realiable Systems from '79:

Todd Hoff said...

That really sucks. Thanks for sharing some of you memories. A quiet competence is a hell of a nice epitaph.

CJ said...

Hi Greg,

I'm sorry for your loss, your father was clearly a very interesting guy to say the least. Being able to share a passion with a father and a son is a gift indeed and you wrote about that beautifully.

Warm thoughts to you and your family.

Jason Crawford said...

Greg, I didn't know your father, but now I wish I had. Thanks for a thoughtful portrait of his accomplishments and his impact on his children and the world.

Paul said...


I'm very sorry to hear your father died. I worked at Xerox SDD from 1976 to 1981 on the Pilot operating system for the Star (see ACM). I did not work directly with your father, but he was a friendly and knowledgeable colleague.

Paul McJones

Sean Murphy said...

I am sorry for your loss.

Quiet competence is a wonderful antidote for our celebrity driven culture.

It's our challenge as sons to carry on alone, preserving the hard won wisdom of our fathers and grandfathers.

Vishal Anand said...


My condolences.

Thanks for writing this proud post.
Can say this as a parent that for all his achievements this would mean more to him than any of his work.

Best wishes to you and your family..

Joanna Butler said...

What a beautifully written post. I didn't know your father but I wish I did; it sounds as though he was a great man who achieved many great things. I'm not surprised you and your sister were inspired to follow in his footsteps. So sorry for your loss.

jeremy said...

Greg -- I'm sorry for your loss. It is great to see, though, his influence and passion live on through his children and, as you say, grandchildren.

Anonymous said...

Dear Greg:

Your eloquence reminds me of your mother (who I've know for more than 40 years). She is a special person -- fine, smart and kind -- who always had a way with language.

I was in your dad's company only a few times, but it was enough to know he was a man of quality.

I am so sorry for your loss. You, Jen and your mother were blessed to have had him and now are blessed to have each other.

Roz Potischman

Atul said...

My condolences.I am sorry to hear your loss. May his soul rest in peace.


Dave said...


In the mid 1980s, I worked with your father at Xerox. He and I, along with Larry Garlick and Victor Schwartz, worked for Leo Nikora, managing the group that built some of the first LAN server products ever sold, including email, print/file servers, and what we would now call DNS name servers. He made a lot of important contributions to the architecture and was a good colleague and a friend. I haven't seen him for many years, but was sad to hear of his recent death. He was a good man.

Dave Redell

Chris Sivori said...

Condolences, Greg.

Kelly said...

This is beautiful. His obituary was also amazing. I have been in the presence of a few "inventors" of Silicon Valley-or so I thought- prior to meeting your dad, but now I realize I was honored to meet the man who paved the way for many of them- Mr Ted Linden. I was also honored just to know him as Betty's husband, Jen and Greg's father and grandpa to three cute little ones and to sit with him and see his quiet grin.


MParekh said...

My condolences, Greg...what a wonderful tribute to his memory. Thanks for sharing.

Anonymous said...

It is a wonderful tribute that you reminisce the happy times... As we age, we men seem to always have an arms-length relationship with our fathers, and both fathers and sons have our little creases. A father as a mentor is a wonderful tribute indeed. Remember the good times!

Peter Neumann said...

Matt, You have done a wonderful thing for your father by posting your message and letting us add to it. I go back into the 1970s with Ted -- who was seriously involved with secure operating systems and interacted wonderfully with Karl Levitt and me at SRI. He was always pushing us to work on hard problems. He was clear a good father and a joy to your mother. Please help her through what must be a very difficult time. Best wishes always. Peter Neumann

Peter Neumann said...

Greg, Apologies for my foregoing message. I have absolutely no idea why I referred to you as "Matt". Peter

Stu Katzke said...


I was extremely sad to hear of your dad’s passing—he was a long time friend of mine (over 34 years). Please know that your mom, you & Jen have my sincerest condolences. I will miss Ted very much – he left us much too soon. Your dad & I first met at a briefing I gave at NSA in the early 70’s and, thanks to that briefing, we met again in 1975 when your dad and Denny Branstad (a mutual friend & colleague of both of us) hired me at the National Bureau of Standards (NBS) where they were both moved from NSA to establish NBS’ computer security program.

Your dad was everything you said about him—I couldn’t have said it any better than you did. To me, he was a good friend and mentor. We sat across the hall from each other at NBS, talked often, and worked together on several projects. You mentioned the ACM paper you dad wrote—I recall reviewing several drafts of that paper for your dad as it evolved. It was a fantastic paper. I do not know if it is still available through ACM Computing Surveys, but NBS (now NIST) published a version of the paper in August 1976 that is still available at:

After he and your mom moved to Palo Alto, we maintained our friendship as best we could living on opposite coasts but we tried to see each other when we traveled to each other’s side of the country. I fondly recall the times I visited with Ted & Betty (most of the time on business-related travel), as does my wife Viv when she had the opportunity to travel with me.

It is difficult for me to accept that Ted is no longer with us but he leaves a professional and personal (i.e., his extended family) legacy that I am sure you are all extremely proud to be part of. Ted was, above all other things, a loving family oriented person & I know he thought the world of all of you. During our most recent discussions, the primary topic was not “work”, but family.

As a closing thought, while Ted has physically departed this world, he lives on in all of us that knew him.

Stu Katzke

Anonymous said...

Greg- My condolences and thanks for sharing ... he will be missed .. I'm sure you and your sister will do him proud

Leo Nikora said...

I remember your dad well. I'm sorry he's gone.

shannonm said...

Dear Greg,
What a beautiful writer you are. Your father was a wonderful, gentle, unassuming and obviously brilliant man. And he and your mother certainly created loving prodigy. He passed away on my birthday, and for some reason I did not see the notice until today (almost a year later). I know you will especially miss him this time of year.
I was a Star Consultant at Xerox - but I also started the Hug Monitor program. I am sending you and yours hugs.
Many blessings for the holiday season and always.

supercharn said...

Hi Greg - I just found your article while I was googling for "haunt" and "parc". My dad worked at PARC also, and he would bring me and my brother in on weekends and we would log into the mainframe from empty offices. I loved Haunt and Maze War. I remember the Alto and the Dandelion and those gigantic hard drives (1 megabyte of information on something as small as a car's wheel!). My dad was a gifted programmer who passed away 2 years ago as well. I think of him every day. Thank you for your post. It has brought a big smile to my face!