Hiram J. Simpson was a sharecropper in Springfield during the antebellum era, working under the plantation owner Colonel Burns. He was married to Mabel Simpson, but after he betrayed Virgil, Mabel divorced him. He is even an ancestor of the Simpsons. He is also the father of Eliza Simpson, who is an ancestor of the Van Houten Family.
At some point, he began working for Wainwright Montgomery Burns as a sharecropper. He was the first husband of Mabel Simpson, and they had one child, Eliza Simpson. The family worked with the underground railroad, helping slaves flee to Canada.
Hiram, despite trying to stand by his oath to help Virgil, turned against his family and slave under their care, by betraying Virgil to Colonel Burns in exchange for a new pair of shoes. Mabel, however, left her husband to help Virgil escape to Canada, and fell in love with him along the way. Mabel divorced Hiram (getting one of his new shoes in the settlement although he kept the laces) and then married Virgil beginning the family tree from which the modern-day Simpsons descend (apparently, after their divorce, Hiram became grumpy and annoyed, as evidenced by the photo below).
Through Eliza Simpson, he is an ancestor of the Van Houten family but not the modern Simpsons themselves. Since Virgil's position in the family is the great-great-great-great grandfather, it is possible that Hiram and Eliza are related to the generations from The Simpsons Uncensored Family Album that came before the Hiram-Virgil cutoff. According to Abe, his family kept Virgil's existence a secret to avoid racist remarks at the time, which they may have also tampered with the family tree (such as removing Hiram, Mabel and Eliza from the tree) to deny any affiliation with Virgil.
It is unknown when Hiram died, or if he continued to work under Colonel Burns after his divorce. It is unclear if he was alive by the time Eliza married Milford Van Houten.