Graham O'Brien is the widower of Grace O'Brien, the stepfather of Aaron, the step-grandfather of Ryan Sinclair, a companion of the thirteenth incarnation of The Doctor and one of the protagonists of the eleventh and twelfth revial series of Doctor Who.
He is portrayed by Bradley Walsh.
Graham was born in Essex, England sometime in the 1960s to an unnamed couple. After his mother's death, Graham's father got rid of her things, unable to kept them.
Graham later became a bus driver before later retiring.
He previously suffered from cancer and was cared for by his chemo nurse Grace, whom he fell in love with. Graham later moved in with Grace at her home in Sheffield and eventually married her.
Graham became step-grandfather to Grace's grandson Ryan, whom Grace was caring for following his mother's death. Whilst Graham treated Ryan as if he was his biological grandson, Ryan was unwilling to accept him as his new grandfather and would refer to Graham by his name rather than Grandad.
In the first Series 11 episode "The Woman Who Fell To Earth", set in 2018, Graham and Grace attempted to help Ryan ride a bike as he struggled to do so due to having dyspraxia. After failing to ride the bike, Ryan throws the bike away in frustration, but goes to retrieve it.
Graham, Grace, Ryan along with Ryan's old schoolmate Yasmin "Yaz" Khan later encounter newly regenerated Thirteen Doctor and help her defeat an alien named Tzim-Sha, but Grace dies in the process.
To cope with his grief, Graham choses to become a companion for The Doctor along with Ryan and Yaz.
In the episode, "The Battle of Ranskoor Av Kolos", Graham encounters Tzim-Sha again and considered killing him to avenge Grace's death. However after The Doctor told him that she would not travel with a killer, Graham along with Ryan instead imprison Tzim-Sha in a statis chamber and told him to think of Grace.
In the 2019 New Year Special "Resolution", Graham and the others encounter and defeat a Dalek.
Graham is the second character Bradley Walsh has played in the Doctor Who franchise after previously portraying The Pied Piper in Doctor Who's spin-off series The Sarah Jane Adventures.