endorser (n.)

• abettor
• admirer
• advocate
• aficionado
• angel
• apologist
• approver
• backer
• buff
• champion
• cosignatory
• cosigner
• defender
• dependence
• exponent
• fan
• guarantor
• insurer
• lover
• mainstay
• maintainer
• notary
• partisan
• party
• patron
• promoter
• protagonist
• ratifier
• reliance
• second
• seconder
• sectary
• sider
• signatory
• sponsor
• stalwart
• standby
• subscriber
• support
• supporter
• sustainer
• sympathizer
• underwriter
• upholder
• votary
• well-wisher