主たる目的は、新市場への参入です。
The main objective is to enter new markets.
He is the principal person in charge of this project.
The main cause of the accident was carelessness.
Derived from the kanji 主 (しゅ, 'main') combined with the classical auxiliary verb たり (たる, attributive form of たり), which functions like modern である. The form 主たる is a fossilized rentaishi used only before nouns.