The Gomagog were powerful interdimensional beings. (AUDIO: The Archive) They were counted among the Great Old Ones. (PROSE: Divided Loyalties). In Earth's mythology they were known as giants. (TV: The Stones of Blood). The Bible called them Gog and Magog, while in the Koran they were known as Yajuj and Majuj. (AUDIO: The Archive, The Feast of Magog)
The Gomagog were known to have destroyed many worlds. Some believed them to be a dark emanation of the Archive. (AUDIO: The Archive) They were capable of possessing other beings, such as humans. (AUDIO: The Feast of Magog)
Other references
The Fourth Doctor believed that the myth of Gog and Magog was inspired by the Ogri of the Nine Travellers. (TV: The Stones of Blood). He also encountered an individual called Magog in a parallel universe. (COMIC: The Iron Legion)