I think we all know of John Entwistle, and then the progressive rock guys Chris Squire and Geddy Lee. But who else? I'm thinking of a growling "piano tone" but not slap bass in this case. Embedded YouTube videos appreciated! Jack Casady might be included but he got his growl sound originally on flats from digging in (fret noise) and splitting the signal to an overdriven amp. Check out "Bless it's pointed little head" album.