I have Marcurio has a follower, (The mercenary from Riften) He's a bad ass and all but the only armour he wears that I give him is the Thalmor hooded robes. I tried taking everything off I gave him and just give him Adept Destruction Robes and he just simply refuses to put it on...

Why does he only wear Hooded Thalmor Robes and nothing else I give him? Is it a bug? Is it just him? Is there even a fix to this?

Because he's a mage.

Obviously............Did you not read my post? I try to give him better robes that help him be a better mage but he sticks to the 12% reduction in Destruction of the Thalmor robes rather than other robes that give a better bonus.

Maybe he's secretly a Thalmor supporter?

All the AI considers is base armor rating, nothing else.

Man i searched around for the answer and i can't find it. Probably a glitch or that is the best robe that you can find for him. Usually followers use the best equipment that you give them

This right here.

Yeah, try giving him enchanted armor. He will put on whatever has the highest armor rating. Robes are randomly selected.

Yeah but the thing is I take everything off of him and just leave him with Adept Destruction Robes and he doesn't even put them on, he would rather wear his base clothes than put them on. On the other hand if I give him Thalmor Robes he puts them on.

I guess it is a glitch considering I never encountered this before.

Hope http://www.uesp.net/wiki/Skyrim:Followers#Follower_Equipment helps.

only thing I can suggest is to enchant a set of armor that fits his skills for him. He should equip the armor where it has a higher armor rating then the robes