Listen Ford, if you just tell me that equation, finally your dimension will be free! Anything will be possible! I'll remake a fun world! A better world! A party that never ends with a host that never dies! No more restrictions! No more laws! You'd be one of us! All-powerful! Greater than anything you've imagined, and all I need is your help!
~ Bill Cipher attempting to strike a deal with Stanford Pines
Deal Makers are beings (usually demons or evil gods) who make Faustian bargains with people. They usually hold up their end of the bargain by helping the victim gain their desire in some way, and the victim is usually very happy with what the villain has given him/her until they need to pay back their end of the deal (usually their soul or something else very important to them).

Deal Makers can also be villains who invite the hero to join them.