Doohan is a Cowboy Bebop character, he was an experienced ship mechanic and manager of a shipyard on Earth.
Doohan built the Swordfish II and, at one point, decided to give it to Spike Spiegel.
Doohan's name is a reference to actor James Doohan, who played Star Trek character Montgomery "Scotty" Scott, the chief engineer of the U.S.S. Enterprise.