One of my favorite's was pretty much a professional replacement or gun for hire the first decade of his career. That's Steve Vai, he started working for Frank Zappa at 18 becoming his first "stunt guitarist," then replaced Yngwie Malmsteen in Alcatrazz, then formed the David Lee Roth band inadvertently replacing Eddie Van Halen as DLR's guitarist and then did a stint in Whitesnake before going out as a solo artist.
David Lee Roth and Ozzy are neck and neck for finding the most guitar talent.
Ozzy had Randy, then got Brad Gillis (Night Ranger) for about 5 minutes, then Jake E Lee and onto Zakk
DLR went from EVH, Steve in his solo band, then Jason Becker and then near the end of the 90's, John 5.