Paul "Paulie" Pennino is Adrian's older brother and Rocky's best friend, later becoming his brother-in-law when Rocky marries Adrian. He is one of only four characters to appear in the first six films (along with Rocky, Tony "Duke" Evers, and Stu Nahan). Young was nominated for the Academy Award for Best Supporting Actor for his performance in the first film, along with co-star Burgess Meredith.
He works at a meat-rendering facility and is portrayed as having a drinking problem and tending towards self-pity, immaturity and emotional outbursts. Though he cares for his friends and family, he is often jealous of their happiness and success and feels they owe him. Paulie is seen to be racist; in Rocky III he openly stated that he did not like any of the black boxers in the gym where Apollo Creed once trained. He also says in Rocky Balboa that "Italian food cooked up by a bunch of Mexicans ain't so special."
Paulie introduced his sister, Adrian, to Rocky and encouraged their relationship. Paulie also invited Rocky to begin his unique training method of punching sides of beef at the rendering facility. After Rocky marries Adrian and struggles to make a life outside of boxing, he recommends Rocky for his former meat packing job; he also buys Rocky's car from him after the latter is laid off. He is disappointed later when he sees Rocky training amateurs in Mighty Mick's Gym; Paulie visits the pet shop where Adrian works and yells at her for refusing to let Rocky continue his boxing career; the stress of the argument causes her to go into premature labor, giving birth to Robert, Paulie's nephew. He later keeps Adrian company on the night of Rocky's rematch with Creed, where Rocky wins the world heavyweight championship.
Rocky, now heavyweight champion, wins a number of succeeding matches and becomes increasingly wealthy and famous. Paulie becomes jealous of Rocky's success, and is arrested after drunkenly destroying a pinball machine with Rocky's image. Rocky bails him out, but Paulie is still angry, claiming Rocky owes him. Paulie briefly attempts to fight Rocky, who easily evades him, and finally asks him for a job. Rocky agrees and hires him as a cornerman. After Rocky's loss to Clubber Lang and the death of Rocky's manager Mickey, Paulie accompanies Rocky and Adrian to Los Angeles, but complains about the flophouse they are staying in, which annoys Apollo. Paulie is again in Rocky's corner as Rocky wins the championship back from Lang.
After Apollo Creed is killed in the ring during an exhibition bout with Soviet boxer Ivan Drago, Paulie accompanies Rocky and Tony "Duke" Evers, Apollo's former trainer, to Siberia to help Rocky train for his match against Ivan Drago. As before in Los Angeles, Paulie gripes about the weather and the austere conditions of the cabin in which they will be staying. Prior to Rocky's match against Drago, Paulie tells Rocky of the admiration and love he has for him. Rocky defeats Drago to avenge Apollo's death.