- "Do you know where God is? … In your heart."
Brian Marcos is the son of Elena Neves and Dominic Toretto, the stepson of Letty Ortiz, the nephew of Jakob and Mia Toretto, and the cousin of Jack and his younger sister. Marcos was kidnapped along with his mother, Elena, and used to blackmail Dom into betraying his crew and cooperate with Cipher, a notorious cyberterrorist keen on starting a nuclear war. However, he was later rescued by Deckard and Owen Shaw. After the rescue, Dom named him after Brian O'Connor.
Marcos was conceived during the time his mother Elena was still romantically involved with Dominic Toretto. Shortly after Luke Hobbs reported that Dom's wife, Letty Ortiz, survived the assassination thought to have killed her, Elena learned she was pregnant. Elena gave birth to Marcos and proceeded to raise him on her own.
When Dom and Letty departed for their honeymoon, Elena intended to reveal the existence of Marcos when they returned from Havana. However, she and Marcos were kidnapped by Cipher and subsequently used against Dom to force him to work for her.
When Cipher allowed him to see Elena and Marcos, she explained the circumstances of his birth to Dom and that his middle name was "Marcos". She thought the honor giving him a first name should go to his father and asked Dom to protect their son no matter what happened.
When Dom fails to cooperate with Cipher, Marcos' mother was killed by Connor Rhodes and Cipher continues to hold him hostage. Marcos is later rescued through the combined efforts of Deckard and Owen Shaw. This allows Dom to save Letty's life by making Rhodes miss his shot on her and then kills him, avenging Elena's death. Following Cipher's escape, Marcos is reunited with his father and Dom names him "Brian", after his friend, Brian O'Conner.
Brian lives with his Dom and Letty at their isolated farm house in London. He helps Dom repair a tractor and then a water heater but they are interrupted by the arrival of Tej, Roman and Ramsey. Not expecting company, Dom instructs Brian to hide as they planned and Brian hides in a small crawl space in the garage.
That night, Dom is putting Brian to bed and he asks where God is, and Dom tells him that God is in his heart. Letty gives Brian her cross necklace and asks him to keep it safe before leaving to join the rest of the team in Montequinto. Dom leaves Brian with Mia and joins the rest of the team.
When the team are attacked in their warehouse, Dom has a vision of Brian asking when he'll be home.
When the team return to Los Angeles, Dom takes Brian to the tracks and tells him about how he learnt everything he needed in life on the track. They gather for a barbecue and Dom asks if Brian is ready to say grace but Brian says he doesn't know how, to which Dom responds "say what is in your heart". Dom instructs Brian to hold as there is a empty chair next to Mia and they all turn to the driveway as Brian O'Conner arrives in his Nissan Skyline.
- According to Elena, she learned she was pregnant with Marcos following the events of Fast & Furious 6; Elena and Dominic's relationship ends around the same time. Fast & Furious 6 takes place in 2013, following the events of Fast & Furious in 2009 and Fast Five in 2010. Marcos conception would have been in 2013, which would not make him an infant, but a child during the events of The Fate of the Furious.
- Marcos is accredited as "Baby Toretto" in the credits.
- He is the son of a woman and a man who have never married.