He was one of the representatives of television summoned after Sideshow Bob threatened to detonate a stolen atomic bomb unless Springfield rid itself of TV.[1]
When Snowball II was the mayor, Lisa canceled out one part of the constitution, subsequently banning all guns. This led to a British Invasion, with Springfield falling under the British flag and becoming a British city, with every law being replaced by its English equivalent. The Springfieldians then started the New Revolutionary War to try and chase the British out of town, to which the British retorted by throwing hot chips at them. With Springfield's citizens all but ready to surrender, Lisa saved the day by simply politely asking the British to leave. With Springfield reinstated as an American city and with Quimby as its Mayor, the British headed back to England. The Doctor was a member of the British invasion.[2]
Many different actors have played the Doctor since Doctor Who began in 1963, but the character design is based specifically on Tom Baker with the trademark long scarf who played the Fourth Doctor from 1974 to 1981.
THOH – "Treehouse of Horror X" (Desperately Xeeking Xena)
Episode – "Murder, She Boat" (costume)
Book – Lisa Simpson's Guide to Geek Chic (mentioned)