Earth Defence Force

According to Group Marshal Nathan of the Tenth Sontaran Battle Brigade, someone named Gareth Jenkins was the leader of the Earth Defence Force that defeated the Sontarans in their invasion of Earth in 2001. When they met a Gareth Jenkins in The Doctor's TARDIS, the Sixth Doctor suggested that the Gareth Jenkins of the Earth Defence Force might not be the same individual present with them. (HOMEVID: A Fix with Sontarans)