Who was the pirate who killed Zephyrs crew?

The Warlord who killed Zephyr’s crew is not named even in the current chapter of the manga. Nevertheless, it was stated that the pirate who killed Zephyr’s crew became a warlord during the timeskip. Therefore, there are only three possibilities: Trafalgar Law, Buggy and the currently unnamed warlord.

Was Z an Admiral?

Z, also known by his birth name and former epithet “Black Arm” Zephyr, was the leader and founder of the Neo Marines as well as a former Marine Admiral and instructor before his resignation. He served as the main antagonist of One Piece Film: Z.