Who are the followers?
In the sanctuary of the journey you will encounter three followers; Templar, the Witch and the villain. Templar heavy armor, strong role, they play a damage absorption or support the treatment of role. Witch is mainly for remote output, could also play a special auxiliary role. The villain is the Diablo ronin (Rogue), reprinted in God - the ordinary crossbow as a weapon of remote role, but also can choose to control the damage output or light groups.
What is the difference of the mercenary followers and Diablo 2?
Mercenaries in Diablo 2 or less the same, but the followers of the special role has its own story line, they have their own character, and have their own position in this world. Overall, the followers can develop more custom content, you can give them equipment, and select a different mix of skills to match you play.