Who is Tatsuo Kumagai from Presumed Innocent and what is their importance?

Tatsuo "Painless" Kumagai is the county's inept pathologist. His nickname came from a former chief deputy prosecuting attorney who said that after Kumagai bungled an autopsy, that the only person who found working with him painless was the corpse because it was dead. Kumagai has presence and qualifications but ultimately his supercilious manner is overshadowed by his slipshod work. He pays the price for this carelessness in damage to his career. To the reader, this is no great loss because Painless insults and ridicules other people regularly and is one of the novel's most unlikeable characters.