expression, noun
the most extreme; the epitome; the prime example
Used to single out the most representative or extreme instance of a category. Often appears in the pattern ～の最たるもの or ～の最たる例.
彼の行動は無責任の最たるものだ。
His behavior is the epitome of irresponsibility.
この作品は彼の才能の最たる例と言える。
This work can be called the prime example of his talent.
最たる is a prenominal adjective meaning 'the most' or 'the greatest,' while 最たるもの is a noun phrase meaning 'the most extreme thing/example.'
From 最 (sai, 'most') + たる (classical copula たり in attributive form) + もの (mono, 'thing'). The phrase literally means 'the thing that is the most.'