Masterplan started as a side-project for Helloween guitarist Roland Grapow and drummer Uli Kusch, but unfortunately it may have gotten them fired from the band.
Blind Guardian is often credited as one of Power and Speed Metal's founding fathers. They were singing about fantasy subjects found in J.R. Tolkien books way before it was cool again in the 2000's.
"Sinner" is a German band that has been around since the 80's by Mat Sinner, who has kept the project going for around three decades now. I call it a "project" because Mat is the only consistency in the band over the years.
Kamelot has become one of the biggest names in Progressive and Power Metal over the years due to the relentless dedication of American guitarist Thomas Youngblood.
Back in 1992 Motorhead went ahead and put out probably their most commercial sounding release ever called "March Or Die", including a ballad with Ozzy and Slash.
Van Halen has always been known as more of a "Party Rock" band than Metal, but their style, larger-than-life persona, massive arena shows, and of course Eddie's guitar was a very influential force on Heavy Metal. Thousands of kids picked up the guitar because of Eddie, he was right behind Jimi Hendrix as far as influential and exciting players...
Ozzy Osbourne... what can you say that hasn't been said. The fact that he's still alive is amazing in itself. He's smoked, injected and drank just about everything. He's bit the heads off a bird and possibly a bat. His first run with Black Sabbath helped form Heavy Metal as we know it today...