E.T. was an extra-terrestrial. According to some accounts, he was a fictional character and the subject of the film, E.T. the Extra-Terrestrial. (AUDIO: And You Will Obey Me) However, a dissenting account presented E.T. as a real individual who once met the Twelfth Doctor when they were both guests on a show hosted by Supergirl, a third alien. (WC: Supergirl Meets E.T.)
E.T. came to on Earth aboard a spaceship and became stranded there. He was taken in by a kindly human family and subsequently used his superpowers (such as his ability to levitate) to become a force of good on the planet.
Supergirl hosted a profile about him on Meet That Hero!, during which she noted several parallels between his life story and her own. At the conclusion of this profile, E.T. presented her with a Kryptonian singing flower he had grown using his abilities. Overjoyed, Supergirl declared that they should form an "alien club". The Twelfth Doctor, also present at the shooting, enthusiastically agreed, offering the services of his TARDIS to help. E.T. was fascinated by the blue box, letting out an appreciative: "Phoooone…". (WC: Supergirl Meets E.T.)
In 2006, after a spaceship landed in the River Thames, people celebrated all over London, especially on the Powell Estate, where some residents put up a banner saying "ELLO E.T.", a possible reference to the character or just to extraterrestrials in general. (TV: Aliens of London)
Behind the scenes
E.T. is a playable character alongside the Doctor and characters from multiple other properties in LEGO Dimensions. The webcast Supergirl Meets E.T. implicitly sets itself in the continuity of LEGO Dimensions, thus with the understanding that E.T. and the Doctor are from different dimensions in the multiverse: E.T.'s Earth is not the one from N-Space. In addition, the E.T. in the game is not quite that from the original film's universe, but a rebooted LEGO version with a materially different history and some unique abilities.