-ator

1.
a combination of -ate1. and -or2. that forms nouns corresponding to verbs ending in -ate1, ,denoting a human agent (agitator; mediator; adjudicator) or nonhuman entity, especially a machine (incubator; regulator; vibrator) performing the function named by the verb.
Compare -tor, -or2 .
Origin
< Latin -ātor, orig. not a suffix, but the termination of nouns formed with -tor -tor from verbs whose stems ended in -ā-; in English, Latin loanwords ending in -ātor have been reanalyzed as derivatives of the past participles in -tus (see -ate1) and a suffix -or (see -or2), and many new English nouns derived from English verbs based on Latin past participles (e.g., vibrator from vibrate)
British Dictionary definitions for -ator

-ator

suffix
1.
a person or thing that performs a certain action: agitator, escalator, radiator
Word Origin
from Latin -ātor; see -ate1-or1