Joffrey Baratheon' is a major antagonist in the novel series, A Song of Ice and Fire and its adaptation, Game of Thrones.
He is the son of Cersei Lannister and allegedly, her husband Robert I Baratheon. It is later revealed that his biological father is his uncle, Jaime Lannister.
People such as Jon Arryn and Joffrey's uncle suspected that Joffrey was not biologically Robert's because most Baratheons in their family inherit black hair, as the "seed is always stronger" (referring to Baratheon). However, Joffrey inherited his mother's blonde hair.
Joffrey is universally hated by everyone, both in-universe and out-universe, so much that even his own actor despised playing the character. As a result, he retired from acting to avoid any other runins about being pressured into roles like Joffrey.