I actually have two nominees in this category (thanks, Mouse), because I couldn't decide between them.
I think bass players tend to be overlooked, other than those few who are front men (e.g. Paul McCartney), and that's a shame because they are absolutely essential in Rock music especially.
My first nominee is a front man, and that's one of the reasons I nominated him- Geddy Lee of Rush. Geddy is tremendously talented; in addition to singing, playing bass and synths (sometimes all three at the same time), he shares songwriting duties with Alex Lifeson on Rush's music. If you've never seen Geddy in action, here's an example:
https://www.youtube.com/watch?v=Hd8cs_vF9LQ
My other nominee is Garry Tallent of the E Street Band, aka The Funky White Boy, or Funk for short. (Garry was given the name when he was the only white guy in a band called Little Melvin and the Invaders.) Now that Danny Federici and Clarence Clemons are gone, Garry has played with Bruce the longest of anybody currently in the band. Garry is a walking Rock and Roll encyclopedia, and he and Southside Johnny Lyon reportedly share a record collection of some 10,000 items. When Bruce would be getting ready to play a classic old rock and roll cover for some audience request, he would often look to Garry for the key.
Here's an old song from a precursor to the ESB, the Bruce Springsteen Band (Springsteen, Tallent, David Sancious, Vini Lopez, Steve Van Zandt), called "Funk Song" (Funk says, "Right On"

):
https://www.youtube.com/watch?v=exYtsG-EqBQ
Garry also has the distinction of being one of the few musicians ever to play a tuba in a rock band, on Bruce's "Wild Billy's Circus Story". In addition, he has had a career in Nashville as a record producer and session musician.