Ingram Plisken is a Time Diver. The mantle of time diver is passed on through some kind of transfer in whatever Astranagant variant the successor is in at the time.

Dr. Who is a Time Lord. He regenerates into new forms by a transfer of energy in the TARDIS.

What if, by some strage coincidence, there was one other Time Lord who survived the destruction of Galafre? What if that Time Lord's TARDIS was broken, and could not decide where and when it ended up in the multiverse when it travelled? In a last ditch to make it out of the Time War, he flung himself and the TARDIS into a different dimension by harnessing the power of a secret he'd been entrusted with, an cylinder of infinite length? And what if, after this, he emerged near the planet Balmar, fusing his TARDIS with the passing mech of one Balmarian man named Ingram Plisken?

What if Ingram Plisken is actually the missing brother of The Doctor, seperated at birth by war and a cruel fate? What if, after surviving this ordeal, he realized he was not a man who was a lord of time, but rather one who could merely dive through it, doing his best to preserve and protect the dimensions?