David Samuel Notkin, whose technical, educational, and social contributions to computer science and software engineering research made him a major figure in the field, died on 22 April 2013, at his home in Seattle, Washington. He was 58 years old. The cause of his death was cancer. David is best known for his research, with his many graduate students, on software evolution. He asked why software is often so hard and expensive to change, and he worked to reduce the difficulty of software evolution to an essential minimum. This focus came from his belief that the ability to change software - its softness - is where its true but under-realized potential resides. He asked questions such as whether we can identify and close the gap between Brooks' notions of accidental and essential software complexity? How much should rather than does it cost to develop, test, and evolve software? Can we make the cost of change proportionate rather than disproportionate to the apparent complexity of changes to be made? Can we design software analysis methods that realize the best properties of both static and dynamic analysis techniques? Beyond technical contributions, David is widely recognized and admired for his exceptional skill as a research mentor for graduate students and as a powerful and unwavering advocate for improving gender diversity in computer science. A brief biography is given highlighting Notkin's professional achievements.