How to control 2 different classed characters?

[Cranthis]

So, not including Dvati (which are same classed), Leadership, Thrallherd, and Undead Leadership, what ways are there to basically have a second character, and play them at the same time?

[Toliudar]

Druid/Ranger gets an animal companion. Wiz/Sorc with a familiar. Psionics with a psicrystal. Paladins/Blackguards get mounts/companions. Anyone can hire help. All of these give you a second character. How powerful/complex/invested with personality that character is becomes a negotiation between you and the DM.

[Edge of Dreams]

The Pathfinder Summoner class (http://www.d20pfsrd.com/classes/base-classes/summoner) gets a creature called an Eidolon that he can summon any time, with unlimited duration. The creature gains hit dice as the Summoner gains levels. It also gets "evolution points" that the Summoner can spend to give the Eidolon (and eventually himself) things like extra limbs, more natural attacks, improved ability scores, and special abilities like flight, scent, etc.

Usually, the Eidolon gets built like a melee monster or Fighter, while the Summoner himself focuses on casting buff, debuff, and utility spells. It's also possible to give the Eidolon lots of skill ranks and bonuses, turning it into a sort of Rogue-like character.

[JaronK]

Anyone who can cast Animate Dread Warrior can have as many PC classed characters as they want, really.

JaronK

[Psyren]

Druid/Ranger gets an animal companion. Wiz/Sorc with a familiar. Psionics with a psicrystal. Paladins/Blackguards get mounts/companions. Anyone can hire help. All of these give you a second character. How powerful/complex/invested with personality that character is becomes a negotiation between you and the DM.

To build on this answer, these creatures were actually designed to be add-ons or supplements to your actual character; however, power creep and splats have led to multiple optimization techniques that turn them into being as powerful as full-fledged characters in their own right. The basic skeletons are there - they get an intiative, they get actions, they get skill checks, they occupy areas on the battlefield - all the rest is just tweaking numbers through feats and buffs to make them viable on their own.