ductor

Ductor, ductoris, m., third declension, an agent noun off duco: the one who leads. Latin already had dux for that job, so ductor stays largely a poet's word - Virgil uses it of Aeneas and of the Trojan captains - and later prose picks it up for a guide or a commander where dux would sound too much like a title.

It is formed the ordinary way: take the supine stem duct-, add -or, and you have the doer. Scriptor from scribo, victor from vinco, lector from lego, all the same machine. English never borrowed ductor itself but took plenty from the stem: conduct, conductor, ductile, and the anatomist's duct, the channel that leads something somewhere.