 Complete the following phrase:  Mr. Burns extreme old age is a frequent source of humor on the show. He is occasionally referred to as Springfields oldest resident; in Season 2s Simpson and Delilah, he told Homer that he is 81, although, in several later episodes, he is shown to be 104. When Smithers informs him that Mr. Burns credit card PIN is his age, he types four digits in his answer. When Lisa Simpson is researching her ancestors from the American Civil War, she comes across a Colonel Burns in the journal, presumably one of Mr. Burns earlier ancestors. However, when Lisa mentions him, Mr. Burns replies by saying that he hasnt heard his fathers name in years. The episode reveals that Mr. Burns father was a slaveowning Southern plantation owner who inspired the character Simon Legree from Harriet Beecher Stowes novel Uncle Toms Cabin, and that Homer and Grampa are descended from Colonel Burnss runaway slave Virgil who fled to British Canada with Mabel Simpson on the Underground Railroad. In other episodes, Mr. Burnss birthplace is apparently Pangea, his national anthem implies he was both from Austria-Hungary and unaware of its collapse in World War I, and he mentions the possibility of an update on the 