No surprise that for Dream Theater‘s John Petrucci it was Rush:

What was the first band you obsessed over?
Probably Rush. I started to get turned on to a bunch of different bands when I was in middle school/high school. I was turned onto The Who and Black Sabbath and Yes, and stuff like that. But Rush I obsessed over. I wanted to have every album. I wanted to know storylines, read all the lyrics, learn the songs and everything. So that was definitely the first one.

Was it with 2112?
Well, I first got turned on to them with Hemispheres. Songs from Moving Pictures were on the radio, but I didn’t really follow it. A friend of mine who was really into them was like, “Oh, you gotta listen to this song.” That’s where it all started.

“Rush are my biggest influence and favorite band”;

“to this day, I apply all of this information to my own style”