executor (n.) Look up executor at Dictionary.com
c.1300, "person appointed to see that a will is carried into effect," from Anglo-French executour, from Latin executorem/exsecutorem, agent noun from exsequi/exsequi "follow after; carry out, accomplish" (see execution). Fem. form executrix is attested from late 14c. (executrice).

Compare executioner, and also executant "one who does or performs" (especially a musical performer), from 1858; executer "one who performs" (1530s).