A
musically inclined person who, instead of being a showman (like most guitarists, but not all) is more the pure musician along with the drummer, the pianist, and the mandolin player, the "musician in the group.
But the main job (this, coming from a bass player) is to translate the
languages between the guitarist and the drummer, for they speak two totally different languages.
And popular to popular opinion, the bass player does not usually create the rhythm or even state it for the guitarist to play along with, it is the drummer that does that in most
circumstances. The bass player in most occasions adds to that rhythm and makes it more complex, or creates a bas(s)is for drum solos.