Lat. hadrianus - 'from Adria (a port on the Adriatic sea)'
Adrian remained Guardian for 200 years longer than he was supposed to, as the Vanguard's experiments on the Guardians-to-be stalled his replacement's arrival. At the end of the extra 200 years, he was forcibly expelled by the Tower in the Guardian's Realm and returned to Stark, where he was disoriented by the 1200 year march of history. Adrian was left wandering the streets, alone and confused. He confesses to April that he was actually relieved to be picked up by the Vanguard and imprisoned by them, as at least then he had food and shelter. His face bears wounds, perhaps from mistreatment under the Vanguard, and strange tattoos that may be either a result of his time as Guardian or from his days in Stark. It is possible that, as a Shifter and Guardian-to-be, he was specially marked by his people.
When a dying Burns Flipper gives April the details of the singularity near the Morning Star space station, he mentions that the Vanguard are also taking a 'special package' spacewards with them - April guesses this is Adrian himself, as a Guardian-who-was can still enter the Guardian's Realm. April finds Adrian on the Morning Star and rescues him from a Vanguard cell. From there Adrian travels with her to the Guardian's Realm, as well as giving her a warning about the Three Trials that await any prospective Guardian.
When April tries to enter the Tower it does not react to her touch, and Adrian must use his own hand to open it. He is as surprised as April that she does not appear to be the 13th Guardian, and distracts Gordon while she reunites him with his other half. He then performs the Changing of the Guard ceremony with Gordon, the real 13th Guardian. What happened to Adrian after this is unknown - though, as a Shifter, he was able to leave the Guardian's Realm of his own accord.