His legs have atrophied. It's fairly common among wizards.

Do legs that atrophy generally completely fall off below the knee? I know wheelchair bound people who haven't walked in over a decade and their legs usually just become really skinny - not fall off completely.

Here're my opinions in full, agree or disagree as you will.

THEORY 1:
Sotha Sil had his legs and Chimer appearence when he bacame a god. He then moved away after some time to work and study alone. He got so caught-up in his work that he stopped returning to Red Mountain to renew his divity (which Vivec mentions). Without his divinity his body began to show its age and (since he was hundreds or thousands of years old) began to waste away (there go his legs). He probably made his machine that he is is connected to so as to keep him from dying (as he cannot go back to Red Mountain because of Dagoth Ur and his loss of legs). He was alive yet rotten and old when Almalexia killed him. Then you saw him.

THEORY 2:
Again Sotha Sil stopped going to Red Mountain to renew his divinity. His legs wore away and he made his machine to keep him alive and healthy. But when Almalexia killed him, the loss of divinity and the machine from his body made it go to the age it should be (old, rotten and dark). [Same with Almalexia and Vivec, when they die, they waste away to nothing :biggrin:]

Sotha Sil didn't stop going to the Heart Chamber because he got caught up in his mechanics or anything. He stopped because the Tribunal and their armies got ambushed by a large number of Ash monsters, who stole the Tools and made off with them. This is explicitly stated in the literature Vivec hands the Nerevarine.

I always assumed that as part of his plan to reshape the world in a more 'perfect' image, Sotha Sil extensively tinkered with his own body as well. Look at the Fabricants throughout his laboratories. They're cybernetic - part flesh and part machinery. He's a Machinist. He made himself into a cyborg. He doesn't need legs because he can levitate and because he spends all his time plugged into a computer, controlling his machines who do his work for him.

Look at him in the [NUMMIT] game, instead of relying on an extremely bright picture from UESP! And if you really depend upon the UESP picture for proof, what about http://www.scharesoft.de/joomla/almanach/images/8/84/Sotha_Sils_Leiche.jpg and http://www.scharesoft.de/joomla/almanach/images/a/ac/Sotha_Sil_nah.jpg

Or you can go into the game and look for yourself.

http://i55.tinypic.com/oqhldv.png That looks nothing like a Dunmer to me. The skin is a completely different color.

Also the two pictures you linked just show his armor, how does that prove anything?

Did you actually look at his skin? You can see his hands and arms too. And it's a helluva lot more dunmerish than Chimer. You must also take account to the fact he's not a generic NPC and he's almost as old as recorded history.

Google more images.

It's logical by the process of elimination that Sotha Sil should be dunmer.

It's what I believe, not because the evidence so, but simply because it makes better lore, showing the contrasts of the Tribunal, between themselves and the people of morrowind. .

And that if his skin doesn't look close to Vivec's Chimer looking side and Alamexia's skin, he can't be Chimer. The only other race would be dunmer, which his grey skin more closely resembles.

Besides, I really wouldn't taken the actual ingame meshes without a pinch of salt. I mean, I doubt Todd Howards or MK went up to whoever was designing the textures of Seht's face, and said "Make sure you don't make him look Dunmer.". Personally, I'd take actual evidence of the nature of Sotha Sil's character through books and logic as more convincing than whatever colour the texture artist decided to splash on his texture.

Did you look at his skin? I agree that it does not look like Chimer skin, but it certainly does not look like Dunmer skin either. His eyes aren't even red like the Dunmer in Morrowind.

I'd like to think he looked like a Dunmer while he was alive too, but he looks nothing like a Dunmer in the Tribunal expansion. I don't need to Google more images, what I linked is a screenshot I took myself. I looked all over at him, and he does not resemble a Dunmer at all. Again, he does not resemble a Chimer either. He looks more like an Imperial with pointy ears and has started to decay.

http://www.youtube.com/watch?v=LfWDilXZQEo

That's not armor. That's his metal cyborg body. Huzzah!

Why would a wizard who in all likelihood from the appearance of his gaunt arms and extremely long, curled fingernails be wearing a suit of what appears to be heavy armor? Isn't it more logical to assume this is a part of the interface that connects his body and brain to his super computer?

Here's a pic of my Dunmer standing next to him taken right from in-game, proof that Sotha Sil's skin is not Dunmeri:
http://i51.tinypic.com/b7gw3p.jpg

EDIT: Higher-resolution screenshot uploaded.

That's only proof that his skin isn't the exact same tone as your character's.

The Chimer side of Vivec, and Almalexia's skin tone aren't the exact same color as Altmer characters either for that matter, and by all accounts they are physically similar.

But they're completly different. They share nothing in common. Sotha Sil looks like an Imperial with pointy ears.

His skin is definitely darker than that of an Imperial. It has a distinctive ashen tone. Are you only pretending not to see it? It's definitely not the same skin tone as Almalexia's.

And lest we forget the journal entry:

I have found the corpse of Sotha Sil. The god's body has been ravaged by powerful forces.

I admitt that it is different from Almalexia's. Just as Vivec's Chimer half is different from Almalexia's (slightly). But I'm just saying it isn't Dunmeri.

Again... ravaged by powerful forces.

Ever seen the skin tone of a person who burned up in a car wreck or got electrocuted to death? It's not the normal skin tone. Almalexia hit him like a ton of bricks, probably with her strongest spells.

So there goes all arguments either way. The only time we get to see Sotha Sil is when he is deformed and his skin-tone is different. There is no possible way of knowing Sotha Sil's skin-tone before the attack (by Almalexia).
Unsolvable.

Except, of course, by going back to the process of elimination and what we're told of his character.

Vivec is the first Tribune we see. He is half Chimer tone, half Dunmer. Next we meet Almalexia in her golden hued glory. Next we meet a badly mangled and burnt Sotha Sil...Dunmer skin tone under all that?

Possibly.

We're told he's the one who talked to the Dunmer after their transformation, comforting them. Vivec also states he cares for the Dunmer more than either he or Almalexia. It stands to reason he'd want to comfort them in part by altering his skin tone to match theirs.

Yes. That may well be true. But we only have speculation until one of the devs tells us...
*crosses fingers*

(Or it could just be left a mystery; like the Dwemer, Sotha Sil's legs, etc.)

Is this like how you remembered making up the connection between Telvanni long-life and necromancy?

"'Sotha Sil,' said a serious-looking Dunmer in a white cloak, shaking the Prince's hand and showing him to a seat."http://www.imperial-library.info/content/morrowind-2920-last-year-first-era

That's because Chimer were Aldmer, slightly different from modern day Altmer.

This is actually really simple. The in-game mesh supports neither supposition, because he is neither golden nor ashen. His skin tone is not otherwise mentioned. Now you can decide whatever you want to decide, but there is no evidence to say.