Oswald "Old Tut" Simpson was the husband of "Happy" Dinsdale. They had five children named Orville, Bonita, Elrita, Twitta and Boris.
He looks like his grandson Abraham Simpson, except his smaller face. He is ¼ black, making him a quadroon (given the story Grampa Simpson told in the episode "The Color Yellow").
According to Much Apu About Nothing, he was born in the old country (Which appears to be Scotland or Canada). In "Homer to the Max", Abe claims he traded a mule for the Simpson name, and that that mule went on to save spring break.
This is clearly one of Abe's wildly inaccurate, inconsistent stories due to his dementia, as generations prior to Old Tut already had the Simpson name.
That being said, it is possible that Old Tut simply traded the mule to get his surname back, much like how his great-grandson Homer gets his surname back in the aforementioned episode.