When you start the game, your first quest is to get something to a cleric and he will join you right away if you want. There is also a necromancer and a vampire waiting at the adventurer's inn that will join you and a knight waiting just inside the first dungeon that you have to go through. So if you want, you are starting with 5th level:

Cleric Necromancer Vampire Knight plus whatever character you roll as your own (level 1).

Once off Dagger Wound Island (the starting area) you can also get a 5th level Minotaur immediately. If you know where to go, you can get a 15th level Vampire and Necromancer then too, and also a 5th level dark elf and 5th & 15th level dragons (the 15th you need to fight to get to). The 50th level Dark Elf Patriarch (advertised by others) and a 50th level Champion (Knight) are available as soon as you do them a service, no matter how early you do it. And a 15th level Troll is available in one of the earlier main-line quests.

There are other characters for hire as you progress in the game (availability is determined by how far you have progressed in the main-line series of quests).