AboutOlen, also known as "The Seeker" - a chronomancer, who has made his way through time to cheat Death and undeath itself in the name of love. For his act of heresy against the chief deity of his people, forsaking the brutal dynasty he once was part of and commiting crimes against the laws of time and space itself, he is now a fugitive.
During his chase across realities by his enemies, Olen has handed the torch of his quest to version after version of himself. He eventually decided to stop running, and to fight back: an action which dragged him into the Doctor's path when he was forced into conflict with the Time Agency who'd been alerted to disturbances in the continuum of several timelines.
At some point (it is not known when) Olen "convinced" a rogue TARDIS to help him in his quest. He also remains in possession of other articles of note, including a Vortex Manipulator, Sonic Weaponry including a Screwdriver and most shockingly, The Master's ring.
Though often drawn into conflict with the Doctor, Olen has insisted throughout their relationship that every action he undertakes is for the Doctor's benefit as well as his own. Indeed, Time Agents believe the TARDIS Olen occasionally summons once belonged to a version of the Doctor that was killed in action, though this has never been verified.
Olen first appeared, and is more closely linked, to the journalist Sarah-Jane Smith, a former companion of the Doctor's. She was aware of some kind of confrontation between Gallowglass and The Master. Prior to his outlaw status, he had approached Smith, asking for the Doctor's assistance. When he refused, Olen took the answer with uncharacteristic humility and pragmatism - an illusion that was later shattered when he appeared with time-distorting technology taken from the foes and allies of the Doctor.
Nobody quite knows exactly what is behind Olen's quest across time and space, but the chaos and disorder wrought in his wake is often counterbalanced by the benevolence of his actions.
Olen says he just wants to go home... and that "Home is where the heart is..."