Lou Barlow

Dinosaur Jr's bassist (original era and reunion era), plus Sebadoh and Folk Implosion on the side. Famously fell out with Mascis in 1989, famously reconciled in 2005, and has been back in the band ever since. The lo-fi confessional songwriter thing that got named 'indie rock' in the 90s — Barlow basically invented it on Sebadoh records.