David Farnsworth

David Farnsworth is the Professor Farnsworth's relative from the colonial era, and is branded by George Washington's head as a traitor who produced counterfeit currency. He was Benjamin Franklin's apprentice. goes back in time by licking Washington's head, track down David Farnsworth and confront him before his descendant decks him in the head with a candlestick. Unfortunately, after beating up Farnsworth they inadvertently alter history.

In the alternate timeline in which the British quickly suppress the Revolution, Farnsworth kills Washington, and is rewarded by being named Duke. To return to his time and reverse the chronological damage, the crew licks Farnsworth's head and return to the colonial era, where the crew restores history and the Professor hits David Farnsworth "much, much harder - Perhaps too hard."

Trivia

 * He is based on the real life counterfeiter, who attracted attention from George Washington due to his counterfeiting and was eventually hanged.
 * For some reason, he is shown to be highly durable, and well trained in hand to hand combat, as he held his own in a fight with Leela.
 * The Professor mentioning that he may have hit David Farnsworth too hard implies that he may have killed him despite his existence in the future. It's possible that although David Farnsworth was a relative of the Professor, he wasn't one of his direct ancestors.