Luke Stetson is Lisa's ex-boyfriend at the Lazy I Ranch.
When The Simpsons went to a ranch Lisa was upset everybody there was careless. Suddenly, a boy named Luke appears and Lisa takes a liking for him. Marge was then upset Lisa was growing up. Later Lisa discovered Luke had, what she believed to be, a girlfriend named Clara. When Lisa encountered her while riding a horse and sent her the wrong way. Later, at the barn dance, Luke revealed that Clara was in fact his sister. Filled with regret, Lisa set out to save Clara, who had ended up falling into the middle of a river. Luke seemingly forgave Lisa, or was simply unaware of her actions, before dumping her after she revealed to him that she had believed Clara to be his girlfriend and thus tried to keep them apart.