Randall Curtis is the creator of the Cosmic Wars movie series.
Bart and Lisa write to him to complain about the poor quality of his latest movie, "The Gathering Shadow". They receive only a form letter in return (along with an autographed photo of Jim-Jam Bonks), so the Simpsons take a trip to Cosmic Wars Ranch, where Bart and Lisa meet Curtis in person and remind him that CGI and updated graphics don't necessarily make a good movie.
Taking Bart and Lisa's advice to heart, Curtis decides to rediscover how he made his creation a success by taking a trip to the video store on a Tauntaun. However, he never makes it to the store, as shortly after Bart and Lisa leave Cosmic Wars Ranch, he meets Homer and Marge, who are extremely drunk from wine samples and start to use him as a football, with him threatening them between throws that he's going to tell on them.
Behind the Laughter
Randall Curtis is a parody of George Lucas, creator of Star Wars. His headquarters, Cosmic Wars Ranch, is an obvious parody of Skywalker Ranch, the headquarters of Lucasfilm which makes the Star Wars films. He might be named after the last names of Tony Randall and Tony Curtis. He is depicted as being very short (as short as Bart and Lisa), likely referencing George Lucas' short stature.
According to the credits of The Gathering Shadow, Randall Curtis acted as the voice actor for Jim-Jam Bonks.