Virgil Simpson was a runaway slave of Colonel Burns that young Eliza Simpson unsuccessfully attempted to help escape through the underground railroad; Eliza never discovered the fate of Virgil, whom she felt she had failed. However, Eliza's mother, Mabel Simpson, left her family in order to lead Virgil to Canada personally, leaving behind her treacherous husband, Hiram Simpson. On their journey, the two began to fall in love and even encountered Abraham Lincoln who offered his top hat to conceal Mabel's hair from the authorities. Mabel and Virgil successfully crossed the border into Canada via a bridge upon which Virgil proposed to Mabel. Mabel legally divorced Hiram and married Virgil, who took his wife's previous married name of "Simpson" since he did not have one of his own and "so that Mabel could keep all her monogram table linens". Mabel and Virgil Simpson then had a child, Abraham, who was Grampa Simpson's great grandfather and presumably his namesake.
 Behind the Laughter
The fact that Virgil is a direct ancestor of the modern Simpsons family seems to completely compromise parts of the previously established Simpsons family tree. Specifically, his picture is seen to replace that of Hiram Simpson in the episode The Color Yellow, though in the family tree from the Simpsons Uncensored Family Album, neither his nor Hiram's picture appears at all. According to Abraham Simpson, Virgil's son was his great grandfather, which would place Virgil and Mabel at the branch of the tree already occupied by Garwood Simpson and Clowta Stillman. It is unknown then if this family tree has been falsified, if there are serious errors, or if Abraham Simpson has simply spoken dishonestly about Virgil (perhaps due to his poor memory and apparent dementia). Another factor to note is that Abraham suggested he may have tampered with the family tree to avoid racist remarks that might have been made if Virgil's picture had remained on the tree.
Or it's more than likely due to the fact that Matt Groening released the book back in 1991 and this episode was made in 2010 and is retconning what was established.
In the German dub Virgil was voiced by Crock W. Krumbiegel.