ETYM Latin: cf. French agresseur.
1. A confident assertive person who acts as instigator.
2. Someone who attacks

ETYM French assaillant.
Assailing; attacking.

Someone who attacks; SYN. aggressor, assailant.

Someone who enters by force in order to conquer; SYN. encroacher.

One who offends; one who violates any law, divine or human; a wrongdoer.

ETYM (USA).
A corporate investor who intends to take over a company by buying a controlling interest in its stock and installing new management.