Come my minions, rise for your master! Let your evil SHINE!
~ Rasputin summoning his demons during his song, "In the Dark of The Night"

Summoners are villains capable of either creating or taming other creatures (often magical) to their will; they are often magic users, but do not necessarily have to be.

In short, any villain who utilizes a ready supply of minions (usually of a non-human variety) that they can call forth at any moment (usually in battle) can be added here.