Doohan was an experienced ship mechanic and manager of a shipyard on Earth.
Doohan owned the Swordfish II and, at one point, decided to give it to Spike Spiegel, his assistant at the time. After Spike left, he took on Miles as an assistant, despite his upbeat attitude. Doohan would often dismiss Miles' suggestions about upgrading certain systems, preferring to keep the machine in its own way.
Doohan had a long-term project to fix the NASA space shuttle Columbia. Miles was pessimistic about it, but Doohan was confident.
In 2071, Spike came to the compound for repairs. Doohan characteristically gave a short welcome, and started fixing the Swordfish, barking orders at Miles. Later, when Reggie came to deliver a part for the ship, Doohan also saw a MONO computer Reggie was trying to sell. Skeptical of its origins, he asked him where he got it and, when he described the ship, Spike overheard this and confirmed the computer was stolen by pirates. Spike left to capture them when he got in trouble. When Doohan heard this, he had to help and decided the Columbia was ready. With Miles' help, he got the ship into orbit and captured the Swordfish which was immobilized and out of fuel. Also fortunately, he survived the landing with the others on Earth. 
- 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.
- He appears to be visually inspired by film director Nicholas Ray
- Aircraft in Doohan's scrapyard include a B-25 Mitchell, a Soviet Mil Mi-24 (Hind), an F-22 Raptor, and an F-16 Fighting Falcon. The tank which his assistant drives is an M4 Sherman.