Claim: Vito Corleone is a father.

Fredo -LRB- Frederico -RRB- Corleone is a fictional character in Mario Puzo 's novel The Godfather . Fredo is portrayed by American actor John Cazale in the Francis Ford Coppola film adaptation and in the sequel , The Godfather Part II .   He is the second son of the mafia don Vito Corleone -LRB- Marlon Brando and Robert De Niro -RRB- . Fredo is the younger brother of Sonny -LRB- James Caan -RRB- and the elder brother to Michael -LRB- Al Pacino -RRB- and sister , Connie -LRB- Talia Shire -RRB- .   In both Puzo 's novel and the film adaptations , Fredo is characterized as weaker and less intelligent than his brothers ; he therefore has little real power or status within the Corleone crime family . The infant Fredo had pneumonia . In the novel , Fredo 's primary weakness is his womanizing , a habit he develops after moving to Las Vegas and which earns his father 's disfavor . In the films , Fredo 's feelings of personal inadequacy and his inability to act effectively on his own behalf are character flaws leading to greater consequences .