One who becomes obligated, an obligor, under a negotiable instrument—such as a check or promissory note—by signing his or her name along with the name of the original obligor, thereby promising to pay on it in full.
A co-maker is a type of accommodation party, who is someone who has signed a Commercial Paper to aid someone wishing to raise money on it. An accommodation party lends his or her name to another person and makes a promise to pay the bill or note when it is due if the other person defaults.