An Etymological Dictionary of Astronomy and Astrophysics

A suffix forming personal agent nouns mainly from verbs, as in dictator, genitor, orator.

Etymology (EN): From L. -tor (examples), cf. Gk. -tor (examples), Av. -tar (astar “thrower,” dātar- “giver,” varštar- “producer”),
Skt. -tr (datr- “giver,” dartr- “breaker”)

Etymology (PE): Agent suffix -gar, variant -gâr,
from kar-, kardan “to do, to make” (Mid.Pers. kardan; O.Pers./Av. kar- “to do, make, build;” Av. kərənaoiti “makes;” cf. Skt. kr- “to do, to make;” krnoti “makes,” karma “act, deed;” PIE base k^wer- “to do, to make”).
Suffix -âr, as in parastâr, xaridâr, virâstâr. Agent suffix -andé, used with verbs.