Gaijin

The Gaijin were a race of scientists.

A group of Gaijin attempted to give the gift of immortality to humans in 17th century Japan. They were prevented from doing so by the Eighth Doctor, Izzy Sinclair and Sato Katsura. (COMIC: The Road to Hell)

Behind the scenes

 * is a Japanese word meaning "foreigner", or perhaps more relevant for this context, "alien".