George Oscar Bluth played by Will Arnett is an aspiring magician and older brother to Michael Bluth. He goes by the nickname GOB.
Like much of the Bluth family, GOB is incredibly self-absorbed. He spends much of his time trying to prove that he is better than his brother to win his father's approval, or become a great musician. He always fails.
He is a womanizer and is in relationships with Marta, Ann, and Kitty at various points in the show. He also has a son named Steve Holt from his high school girlfriend. He does not discover that he is a father until Steve is in high school.
His main magical rival is Tony Wonder, played by Ben Stiller. In a convoluted plot Tony and GOB attempt to seduce one another in order to ruin each other's careers. Although both claim they are straight, it seems like they begin to develop feelings for each other. Ann eventually tricks them into having sex with one another.
Even before the Tony Wonder plot, there were multiple hints that GOB is sexually interested in men and women. When his nephew talks about being awkward with a girl, GOB tells him a story about having a threesome with a man and a woman. He also has a flashback to running into a couple on the yacht and it is implied that he had a threesome with them. There are also quite a few moments throughout the seasons where GOB is clearly admiring men.