I became turned off with the Boxing Episode, the Security Guy being a drunk and the metamorphosis thing.
Sinclair was nebulously giving prophetic messages. Where was he, and what happened to him?
Short Answer: He was Valen.
He went back in time, undergoing the same transformation as Delenn (to become Minbari in his case) and then became Valen in that era.
Thanks!
Trying to explain it in terms to someone who’s only seen the first season…
He was Valen, who was the Minbari Christ-figure who led them to victory over an ancient enemy knows as the Shadows in a great galaxy-spanning war a thousand years before. He united the Minbari people, formed the Grey Council, and with the help of the Vorlons other younger races of the galaxy drove them back to their homeworld of Z’Ha’Dum, where they retreated and returned to a state of hibernation. As of the start of Babylon 5, the Shadows had begun to stir again and were about to begin another war with the younger races.
When the Minbari captured Sinclair during the battle of the line, they scanned him with a device called a Triluminary that was linked to Valen (his soul? his DNA? depends on whose version of the story you believe) and found that Sinclair was in some way connected with Valen - possibly a reincarnation. At the very least it seemed that the Minbari and human races were somehow linked - the way that this was explained by the high-level MInbari was that Minbari souls were being reborn in human bodies. The Minbari ended the war just short of the point of human genocide, wiped Sinclair’s memory of the encounter, and returned him to his people, and eventually arranged for him to be assigned to Babylon 5, where he could be watched over by a member of the grey council - Delenn. In attempt fulfil the prophecies of Valen and bring the two races closer together, Delenn eventually used the Triluminary (which was keyed to her biology as she was actually one of the descendents of Valen) to transform herself into a human-Minbari hybrid, as had been predicted by Valen a thousand years before.
It wasn’t until Delenn came to Babylon 5 itself that she realised the truth about Valen, and Sinclair, since she recognised the station as being similar to the base of operations which had been used in the previous Shadow war, which had seemingly appeared out of nowhere after the Minbari’s own base had been destroyed by the Shadows. This mysterious ancient base was actually Babylon 4, which Sinclair and the crew of Babylon 5 stole by travelling through time and sending back to a thousand years to the previous Shadow war. Sinclair had by this time pieced together the various clues about his identity and fate and knew it was his destiny to ride back with Babylon 4, and using the Triluminary underwent a transformation into a Minbari.
TLDR: He was a Minbari that lived a thousand years ago, became a revered religious figure, and set into motion a lot of the events driving the series.
Thanks again. 