In the novelization of Rambo: First Blood Part II, John mentions that his father drank and beat his mother, Marie Drago, but this was not mentioned in the film canon. Reevis Rambo also tried to kill John with a knife at one point during a drunken rage, but Rambo defended himself by shooting his Compound Bow at his father, badly injuring and nearly killing him. Rambo would run away that night and later be drafted into the army. The result of this fight led to the two men not speaking for over forty years.
On the boat ride into Burma, Sarah Miller asked Rambo if he has a family back home. Rambo replied that he maybe he has a father. Sarah suggested that he should go back home, but Rambo shrugged it off, content with his life in Thailand. However, after the end of the film, he was encouraged by Sarah's words and went home, where he saw his father's rusted mailbox at his horse farm. Rambo looks back at the road he has been walking since the first film, hesitant to proceed, but then keeps walking, having finally moved on with his life.
Rambo's father is died on 2000 and his grave is seen on the ranch next to Helga Rambo's grave who is John's mother in the film series. The "R. Rambo" mailbox was seen on two occasions in the film, as well as several family photos that may or may not be him. Rambo also revealed in the film that he regretted running away at age 17.
R. Rambo's first name is unknown. Sylvester Stallone has joked that it is "Roberto", which could be a reference the Rocky series of films, which also star Stallone, Rocky's real name is "Robert". But it is believed that his first initial is 'R' because of Richard Cre