Sponsor, patron, surety, guarantor, backer, angel are comparable when they denote a person who in a greater or less degree accepts responsibility for another person or for a particular venture or undertaking.
Sponsor usually implies public acceptance of a responsibility and a definite engagement to perform what is promised; the word implies making a pledge in behalf of another and thereby accepting responsibility for its fulfillment; thus, the sponsor of an infant in baptism makes the promises in the child’s name and pledges himself to be responsible for the child’s religious training if the latter is deprived of his natural guardians.
In a wider sense sponsor suggests assumption of the role of promoter or supporter and may imply acceptance of any degree of responsibility from one that is complete to one that is indirect or remote and often purely economic.
Patron stresses the acceptance of the relation as a protector or benefactor especially in return for service, honors, or devotion; it often implies the obligation to assist, support, or defend; thus, a patron of an artist or of a poet is a wealthy or influential person who makes him a protégé presumably in return for honors paid him; the patron of an institution, a cause, or a charity is one whose generous and regular contributions to its support are publicly recognized.
Surety and guarantor imply answerability for another’s debt or performance of duty in case of default because of prior acceptance of responsibility.
Backer, less specific in denotation than the other terms, is used chiefly in relation to enterprises (as of sports, politics, and the theater); it often implies the giving of financial support, sometimes merely moral support or encouragement, but it carries no implication that responsibility for debts is assumed.
Angel is a somewhat derogatory or contemptuous term for a financial backer, especially of a theatrical enterprise.