Navigator (species)

The s were a highly-evolved phylogenetic life form. One of the planets they originated from was Yisotaga.

Jack Harkness faced them during one of his first missions as a Time Agent.

On 2017, the Navigators were absorbing energy from the heliosphere. Jack explained to Gwen the reason they did this was so they could "seed" life on other planets.

Jack said that they only seedes a new galaxy when they believed the current form of life was reaching its end. (COMIC: World Without End)