Mr. Burns' extreme old age is a frequent source of humor on the show. He is occasionally referred to as "Springfield's oldest resident"; in Season 2's "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 hasn't heard his father's 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 Stowe's novel "Uncle Tom's Cabin", and that Homer and Grampa are descended from Colonel Burns's runaway slave Virgil who fled to British Canada with Mabel Simpson on the Underground Railroad. In other episodes, Mr. Burns's 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 Siege of Khartoum, implying that he was aware of current events as early as 1884. In other episodes, he has instructed a postal clerk to send a telegram to the Prussian consulate in Siam via autogyro, and believes a nickel will buy "a steak and kidney pie, a cup of coffee, a slice of cheesecake and a newsreel, with enough change left over to ride the trolley from Battery Park to the Polo Grounds.” In "The Old Man and the Lisa", Mr. Burns' investment portfolio is revealed to consist of long-defunct and obsolete companies such as "Confederated Slave Holdings", and he learns about the Wall Street Crash of 1929 and the Great Depression for the first time after checking a very old stock-ticker.