Ray (Delta and the Bannermen)

Rachel "Ray" Defwydd was a female mechanic and motorcycle enthusiast in 1959 Wales.

Biography
She was in love with Billy, a professional mechanic and part-time singer at a Welsh holiday camp in Shangri-La. However, her love for him turned out to be unrequited, as he fell in love with the Chimeron Queen, Delta.

Despite this she provided valuable assistance for the the Doctor during his confrontation with the evil Gavrok, leader of the ruthless Bannermen, providing him with transport on a motorbike as he sought to warn Delta about Gavrok's arrival and subsequently helped get her to safety when the Bannermen attacked. (DW: Delta and the Bannermen)

Behind the Scenes
Ray was originally created with the intention that she would replace Mel as a companion due to rumours that Bonnie Langford was leaving the show, but filming and airing schedules meant that Mel actually departed in Dragonfire and was replaced by Ace. (BBC DVD: Survival)

An unofficial book published in 2008, Eclectic Gypsy: The Unauthorised Biography of Doctor Who, opens with an original short story, "The One That Got Away" in which a later incarnation of the Doctor (implied to be the Tenth Doctor) encounters a now-elderly Ray in the 21st century, and regrets the fact that he never took Ray on as a companion.