Affiant

A person that is sworn to an affidavit; who gives evidence by way of an affidavit.

Synonymous with deponent in jurisdictions that prefer the word deposition to affidavit.

Both affiant and deponent refer to the author and signatory of a sworn statement given under oath and containing allegations of fact intended to serve as evidence in judicial proceedings, except that the process of a deposition  differs from the process of an affidavit.

Two persons sign an affidavit, the person setting out the allegations of fact and swearing them to be true, on solemn oath or on a religious oath, and the person administering the oath, the oath officer (usually a lawyer, a notary or a commissioner of oath).