The archetype name you're looking for is Undead Lord.
It -is- a called companion, but it's not treated as a companion for anything. You can design a zombie or skeleton, and it just shambles around to fight for you. Doesn't gain feats, normally.
Now.. Go read Classic Horrors Revisted (namely the Walking Dead section) and the Bestiary sections on Skeleton and Zombie. Skeleton and zombie are templates. Variants exist, though if you do use a variant, you only are allowed half the HD that you would be (for the companion, it is equal to your HD regularly [so half for a variant]). You can use Skeleton Champions, which retain class levels, though they do lose some abilities, Zombie Lords, the zombie equivalent to skeleton champions, and plenty others. You might be interested in the Magus, which is a skeleton that retains its Intelligence and can cast spells.
There is a LOT of versatility if you look through all the rules. I designed a 14th level cleric who went Undead Lord. He had a minotaur skeleton champion who carried around a coffin on his back, which was linked to a demiplane with permanency on it where the cleric kept his undead horde to experiment on and junk. Battle starts, minotaur swings the coffin off and slams it down, then a bunch of different kind of undead stumble out (archery skeletons, magus skeletons, exploding zombies..). Without Leadership, I had an army. If I had taken that feat, it would have just been ridiculous. Necromancers are just plain dirty.
Never did get to play him.