Let's talk about the Vorlons...because there ain't much we can SAY about the Vorlons...because nobody knows anything about them.
In our opening movie, everyone's awaiting the arrival of the fifth and final ambassador (four if you don't count Sinclair) from the primary alien governments. He is a Vorlon, a race we have tried, without much success, to learn about ever since we first picked up their transmissions. Several scout ships were sent on First Contact missions. All of them met with unfortunate "accidents" upon entering Vorlon space. The Vorlons tendered their most sincere apologies.
And suggested no further expeditions.
Now, at last, with B5 becoming functional, and all of the other ambassadors in place, it no longer makes strategic sense to continue in their isolation. So the arrival of the Vorlon is a Big Deal. No human has ever even seen a Vorlon.
And they play it right up to the hilt. The ambassador -- Kosh Naranek -- maintains only audio contact with B5 as his ship makes the long voyage, citing "problems" with video. He clearly doesn't want to broadcast the Vorlon face all over the quadrant. So no problem, after all, he has to arrive eventually, and they'll see him then.
The ship arrives. The Vorlon ambassador emerges from his ship...and well, y'see, he comes from a very different environment. Lots of methane and CO2. Our atmosphere is poisonous to Vorlons. So he emerges wearing an Encounter Suit...which covers every square inch of his body except for his hands -- assuming those are his hands -- with a dark faceplate in the front. The only place he can remove all of that is in his quarters, and there are no vids in his quarters, no way to observe him or see his true face.
So...even now, no human has still ever seen a Vorlon.
Well, that's not entirely true. Legend has it that one human saw a Vorlon. A pilot who crashed, off course, on a Vorlon colony.
According to that legend, the human who saw a Vorlon...was turned to stone. But, after all, it's only a legend.
The Vorlons are the great unknown. They occupy a *huge* sector of space. No expedition ever sent to Vorlon space has ever returned, or sent back word. No human had ever even *seen* a Vorlon prior to Kosh's arrival on B5. Their technology is vastly superior to just about everyone else's. To unravel the mystery, to maybe get a *piece* of their tech, is more than sufficient inducement, I'd think.
We will reveal what Kosh is a LOT sooner than year 5. Closer to the end of year 2.
Is Kosh what he/she/it appears to be?
Kosh is always and forever *exactly* what he appears to be, no less and no more. At the same time, Kosh is absolutely *nothing* like what he appears to be.
These are not contradictory statements.
And this is about the straightest answer I've given yet on the subject, believe it or not.