For me it was Jeff Kinney. I was meeting a different author I love, but there wasn't enough room downstairs and we had to go up. Turns out that's exactly where Jeff Kinney works! He's the author who got me into reading so I thought that was so cool
Numerous metal bands... I can't list them all with any accuracy. In the early 2000s I met most of the Green Bay Packers and numerous WWE wrestlers due to a promotion gig I had.
Small venues offer more opportunities. I also am a musician myself, so being friendly with opening local acts and sometimes doing sound or hell, even sometimes filling in for my buddies if they needed a guitar or bass to step in. I've just been involved in the scene as a fan, a tech, and musician for a long time, it just kind of happens.