So I did some digging and found an LA Times article about him from 1999 that described him as "a truly nice guy" who is "friendly to everyone" and "laid back and relaxed."
According to the article, "Mike Riley seems almost too good to be true."
Riley played for the University of Alabama in the '70s before embarking on a coaching career that's included stops at small colleges (Whitworth, Linfield, and Northern Colorado), major colleges (USC and Oregon State), the CFL, the WLAF, and the NFL (San Diego and New Orleans).
In the words of one player, some coaches are "so serious and so caught up in, ‘Win, win win, drill, drill, drill,’ that you lose the fun in it. And [Riley’s] brought the fun back to the game. Don’t mistake it that he doesn’t have a fiery edge, that he doesn’t have a competitive edge, because he does. It’s just an extremely unique blend, particularly in this business."
According to Riley:
"I like coming to work and I like the good atmosphere. I really like people to feel ownership in something, and along with that I want them to feel great about coming to work. I don’t want them to dread coming in the gate over there. I didn’t want the [my players] to dread coming into the football facility. I want them to feel excited about it."