Implementor vs. Implementer [closed]

They are both corrrct terms, "implementer" is now the more common between the two Ngram. It appears there is no difference in usage between AmE and BrE where implementer is equally common Ngram.

Both -or and -er are common suffixes which are used to make nouns out of adjectives:

-or:

• word-forming element making nouns of quality, state, or condition, from Middle English -our, from Old French -our (Modern French -eur), from Latin -orem (nominative -or), a suffix added to past participle verbal stems.

• In U.S., via Noah Webster, -or is nearly universal (but not in glamour, curious, generous), while in Britain -our is used in most cases (but with many exceptions: author, error, senator, ancestor, horror etc.). The -our form predominated after c. 1300, but Mencken reports that the first three folios of Shakespeare's plays used both spellings indiscriminately and with equal frequency; only in the Fourth Folio of 1685 does -our become consistent.

-er:

• English agent noun ending, corresponding to Latin -or. In native words it represents Old English -ere (Old Northumbrian also -are) "man who has to do with," from Proto-Germanic *-ari.

• Generally used with native Germanic words. In words of Latin origin, verbs derived from past participle stems of Latin ones (including most verbs in -ate) usually take the Latin ending -or, as do Latin verbs that passed through French (such as governor); but there are many exceptions (eraser, laborer, promoter, deserter; sailor, bachelor), some of which were conformed from Latin to English in late Middle English.

Etymonline

they are alternative spellings of one another, so they are equivalent. Having said that, I would prefer

He implemented the library.

Unless you are trying to say something different, like he created and currently maintains the library, in which case something like:

He is the creator and maintainer of the library.

might be better.