Sydney Smith

Sydney was the husband of Verity and the father of John Smith in the fictional backstory the TARDIS gave the Doctor when he chose to become human. They raised John on Broadmarsh Street in Radford Parade in the district of Nottingham. (TV: Human Nature) After he and his wife died the family maid, Martha Jones, continued to serve John. (TV: The Family of Blood)

Behind the scenes
John's parent's names Verity and Sydney were a tribute and reference to Verity Lambert and Sydney Newman, both essential to the making of Doctor Who.