One the aspect I like the most about this man is how approachable and down to earth he still is after all these years. I'll give one example. Late on night, my friends were in the basement of the Gates building at Stanford working on their CS107 Heap Allocator project. Lo and behold, Donald Knuth walks by and sees them drawing all sorts of things on the white board in the hallway. "What's that?" he asks, to which my friend responds about the heap allocator project. "Oh, I know a thing or two about heap allocators; let me guide you" :)

edit: lo and behold!