Rickert is a mage-smith from the Vinheim Dragon School. He was somehow trapped in a cell in New Londo Ruins and can't get out, but he doesn't seem to mind. He specializes in Magic weapon enchantments.
Rickert was exiled from Vinheim, presumably because he became Undead. Not much is known about him except that he considers Big Hat Logan to be a legend dating back to "a hundred years ago", which could imply that Logan was kept from hollowing for so long by his ambition to get his hands on Seath's studies.