Stephen Russell Davies OBE FRSL, better known as Russell T Davies, is a Welsh screenwriter and television producer. He is best known for being the original showrunner and head writer of the 2005 revival of the BBC sci-fi series Doctor Who, from 2005 to 2010 and again from 2023. His other notable works include creating the series Queer as Folk (1999–2000), Bob & Rose (2001), The Second Coming (2003), Casanova (2005), Doctor Who spin-offs Torchwood (2006–2011) and The Sarah Jane Adventures (2007–2011), Cucumber (2015), A Very English Scandal (2018), Years and Years (2019), It's a Sin (2021) and Nolly (2023).

Stephen Russell Davies was born on 27 April 1963 at Mount Pleasant Hospital in Swansea. His father, Vivian Davies (1925–2015), and his mother, Barbara (1929–2001), were teachers. Davies was the youngest of three children and their only son. Because he was born by caesarean section, his mother was placed on a morphine drip and was institutionalised after an overdose resulted in a psychotic episode. He described his mother's experience as "literally ... like science fiction" and an early inspiration for his writing career. As a child, Davies was almost always referred to by his middle name. He grew up in a household that "never switched the TV off" until after closedown, and he subsequently became immersed in dramas such as I, Claudius and Doctor Who. One of his first memories, at the age of three, was the 1966 Doctor Who serial The Tenth Planet. He was also an avid cartoonist and comics enthusiast, and purchased series such as Asterix and Peanuts.

Davies was in a relationship with Andrew Smith, a customs officer, between 1999 and Smith's death in 2018. They entered into a civil partnership on 1 December 2012, after Smith was diagnosed with a brain tumour from which he was given only a 3% chance of recovering. Smith died on 29 September 2018. Years and Years ends with a title card which dedicates the series to Smith.