Gareth (The Age of Steel)

Gareth was to-be the bride of Sally Phelan a woman who was "upgraded" into a Cyberman. Before her death, Sally asked "Where is Gareth?" when The Tenth Doctor and Mrs. Moore broke the emotional inhibitor which stopped the Cybermen from feeling anything.

It is likely that Gareth was also converted into a Cyberman.

It is possible that Gareth was the alternate Gareth in The Doctor's world.