–tōr is an agent suffix:
Herbert Weir Smyth, A Greek Grammar for Colleges (misscanned)
a. The primary suffixes τᾱ, τηρ, τορ, τρο, ευ, denoting the agent or doer of an action, are masculine.
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3. τορ (nom. -τωρ): ῥή-τωρ orator (ἐρέω shall say, ἐρ-, ῥε-), εἴ-ρη-κα have spoken, κτίσ-τωρ founder (κτίζω found, κτιδ-), σημάντωρ commander poet. (σημαίνω give a signal, σημαν-).
-τωρ and its Latin cognate -tor (e.g. gladita-tor, domina-tor, can-tor), is an Indo-European suffix.