"Sibling Rivalry" is the 22nd episode of the fourth season of the animated comedy series Family Guy. It originally aired on Fox in the United States on March 26, 2006. The episode follows Stewie as he battles with his half-brother, Bertram (voiced by Wallace Shawn), who is born to two lesbians after Peter donates sperm. Meanwhile, Lois begins excessive eating after Peter undergoes a vasectomy and loses his interest in sex. The episode was written by Cherry Chevapravatdumrong and directed by Dan Povenmire. The episode received mixed reviews from critics for its storyline and many cultural references. According to Nielsen ratings, it was viewed in 7.95 million homes in its original airing. The episode featured guest performances by Randy Crenshaw, Gavin Dunne, Bob Joyce, John Joyce, Phil LaMarr, Rick Logan, Wallace Shawn, Tara Strong, Nicole Sullivan and Wally Wingert, as well as several recurring voice actors for the series. Plot After Lois has a pregnancy scare, Peter reluctantly agrees to get a vasectomy. Concerned they might eventually want another child, he decides to freeze some of his sperm before the surgery. At the sperm bank, he accidentally destroys all the existing samples, and replaces them with his own. A lesbian couple use one of the samples to conceive a child, giving birth to Bertram, who first appeared in the episode "Emission Impossible". Bertram declares war with Stewie for control over the playground. They confront each other with F-117 Nighthawks and AH-1 Cobras, firing numerous bullets. After the air battle ends with no winner, Bertram resorts to biological warfare, using Stewie's new-found girlfriend to infect Stewie with chickenpox. After recovering, an enraged Stewie confronts Bertram, and they engage in a sword fight in the play area. Stewie eventually wins by disarming Bertram, and later that night, is seen suspiciously digging a hole with Christopher Moltisanti, but the hole is actually for a young tree. When Christopher questions Stewie on what happened to Bertram, Stewie claims that Bertram admitted defeat and ran away, with Christopher calling Bertram a mook. Meanwhile, Peter loses his sex drive after the vasectomy, much to the frustration of Lois, who turns to food. After Peter makes fun of her slight weight gain, she deliberately gains more weight out of spite. Her increased appetite results in her becoming obese, which ironically ends up reviving their sex life. Peter feeds Lois copious amounts of food to make her even