Villains from other worlds have long been a Doctor Who mainstay. Whether the TARDIS has taken the Doctor and their companions into the distant past or the far future, on Earth or elsewhere in the universe, almost every threat the Doctor comes up against is alien in origin. However, one Season 3 monster broke the trend, putting the Tenth Doctor and Martha Jones up against a creature without any trace of alien DNA.
Source：https://www.cbr.com/doctor-who-the-lazarus-experiment-villain/
