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.