George Oscar Bluth, Sr., or "Pop-Pop" to his grandchildren, is the patriarch of the Bluth family and the husband of Lucille. George Sr. was the CEO of the Bluth Company until the SEC started investigating him and he got imprisoned. In prison, George Sr. still tried to control his company through GOB while his competent son, Michael, tried to run it legitimately.
At one point, George Sr. escapes to Mexico with the evidence of him dealing with Hussein and fakes his death. He then sneaks into the Bluth home and lives in the attic, until eventually he is found, and put under house arrest.
By the end of the series, it is revealed that Lucille was the true mastermind and he escapes to Cabo at the end.
(Regarding Buster) Maybe it was the eleven months he spent in the womb. The doctor said there were claw marks on the walls of her uterus. But he was her 'miracle baby'. And I-I was just too burnt out on raising you guys to care. So... He turned out a little soft, you know...George Sr.
George Sr.: They cannot arrest a husband and wife for the same crime.
Michael: Yeah? I don't think that that's true, dad.
George Sr.: Really? I've got the worst (bleep) attorneys!