I can't say it better than Pat Helland:
Being at a conference like HPTS was very entertaining as I could look from across the room and see Jim march methodically through all the attendees, many he'd known for years and some he was just meeting. I would smile because it was obvious they were getting the same kindness and curiosity that I so enjoyed. I knew they would benefit from that attention.
I met a lot of so-called architects or experts who seem to take pride in being hard to understand (after all, if they could be understood by mere mortals, they wouldn't be experts...)
Jim Gray is the exact opposite:
When strangers approached Jim, he had an uncanny ability to assess what they could understand and the level at which to explain the problem. I've seen him take the most complex issues and dissect them into a framing that allowed a lay person to understand the gist of the problem and then, separately, dig int the deepest and subtlest nuances with another more versed in the topic.
I really feel priviledged to have met Jim Gray.