guarantor (n.)

• angel
• approver
• backer
• bondsman
• cosignatory
• cosigner
• endorser
• godfather
• godparent
• guarantee
• guaranty
• insurer
• mortgagor
• notary
• party
• patron
• ratifier
• signatory
• sponsor
• subscriber
• surety
• underwriter
• upholder
• warrantor