Guarantor

n. one who gives a guaranty or security

A surety is a person who agrees to be responsible for the debt or obligation of another. Additionally, the situation in which a surety is most typically required is when the ability of the primary obligor or to perform its obligations under a contract is in question, or when there is some public or private interest which requires protection from the consequences of the principal's default or delinquency. In most common law jurisdictions, a contract of suretyship is subject to the statute of frauds (or its equivalent local laws) and is only enforceable if memorialized by a writing signed by the surety.
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Noun
1. one who provides a warrant or guarantee to another
(synonym) surety, warrantor, warranter
(hypernym) patron, sponsor, supporter
(derivation) guarantee, warrant

(n.)
One who makes or gives a guaranty; a warrantor; a surety.
  

(n.)
One who engages to secure another in any right or possession.
  

A person who pledges payment or performance of a contract of another, but separately, as part of an independently contract with the obligee of the original contract. - (read more on Guarantor)