William (or Irving, possibly William Irving or Irving William) "Sparkplug" Witwicky led a very very interesting life for a working-class guy with little formal education from Oregon.
Marvel Comics continuity
William "Sparkplug" Witwicky was a Sergeant in the US Marines. A P.O.W. during the Korean War, he was forced to repair the Koreans' equipment. However, he secretly sabotaged that same equipment, leading to personnel and material losses for the North Koreans. He was a mechanic and owned his own service station until it was destroyed by Ratbat and the Predacons. It is never established whether or not he rebuilt the station.
Sparkplug suffered a heart attack as a result of the Autobots, and was much less friendly with them thereafter.
Sometimes Sparkplug identified himself as William Witwicky, but other times he identified himself as Irving Witwicky. The most likely answer is that his full name is William Irving Witwicky (or Irving William Witwicky).
At some unspecified point in the past Sparkplug worked as a ruby crystal miner in Burma, of all things.
When first seen in the present day he and and his son Spike were working on an off-shore oil rig. The rig was destroyed in the battle with the Decepticons and the two quickly and happily latched on to the Autobots that saved them, offering up their expertise and knowledge about planet Earth in exchange for joining the team.
Spike and Sparkplug seem to have moved into the Ark after this and are almost constantly seen hanging out with the Autobots, there or abroad on missions. While Spike enjoyed going out on missions frequently, Sparkplug tended to stay at the Ark and help Wheeljack and Ratchet on any mechanical or engineering work they were doing. He was apparently good enough and transformer engeneering/technology/biology to effect repairs on Transformers like Omega Supreme without aid or guidence.
He is kidnapped by the Decepticons as a test subject for Doctor Arkeville and turned to their side by the doctor's mind control chips. This causes Spike much emotional pain until the Autobots eventually find a way to use soundwaves to counter the chips and bring the true Sparkplug back.
Sparkplug was later seen operating a garage in New York.
(Sparkplug appears throughout Seasons 1 and 2 of the cartoon but does not appear in the Movie, set 20 years later, nor is he ever seen or mentioned after that. His fate remains unrevealed.)
Find Your Fate Junior
Sparkplug discovered a critical weakness in the Decepticons' circuits that would allow the Autobots to destroy them once and for all. However, the Decepticons discovered this and came after Sparkplug, who fled to the hills to hide, eventualy leading to an Alamo-like standoff with a small group fo Autobots holding off the Decepticon army from the shelter of a cave for two days while they waited for relief to arrive, with sparkplug performing the makeshift repair work to keep them running.
The paper Sparkplug had the specifics of the weakness on was ruined in the battle. He could re-create the research, but the Decepticons would be able to change the design of their circuits while they did so. Still, at least it would keep them out of trouble for awhile!
While tinkering in his lab, Sparkplug invented the Sun-Pak, a powerful solar battery that threatened to change the balance of power between the Autobots and the Decepticons. Insecticon spies forced them to flee the testing range through a series of caves, and Sparkplug later rescued Beachcomber from Kickback, using a gun that caused Kickback to short out and return to tiny size.
Sparkplug suffered memory damage, and was unable to re-create the Sun-Pak after the prototype was destroyed.
Dreamwave comics continuity
Sparkplug was one of the humans chosen to accompany the Autobots back to Cybertron, but was killed in 1999 when the Ark II exploded.
- Although the Production Bible states that he is a widower, no mention ever seems to be made of him ever having had a wife.