The English agentive suffix is -er or -or. The majority of words are formed with -er, but there are also many formed with -or. The suffix -er is used with words of Germanic origin, and -or is used with words derived from Latin.
Many words are formed with the suffix -er. They include baker, shoemaker, teacher, painter and farmer. In German, these words are Bacher, Schuhmacher, Lehrer, Mahler and Bauer. Notice that they have the same suffix.
With words of Latin origin, -or is used. Examples include professor, actor, director, conductor and narrator. To compare, these words in Spanish are profesor, actor, director, conductor and narrador. They are words of Latin origin.
A few words can combine with either -er or -or. Examples of such words are counseller/counsellor and adviser/advisor.
Many English words are formed with the agentive suffix -er or -or. Though most of these words are combined with -er, a significant number are formed with -or. The words formed with -er are of Germanic origin. This is not only the case in English but also in the Germanic languages of German, Dutch, Danish and Norwegian. A few words can be formed with either -er or -or.