Dark Knight

[Tsukino]

All these folks upset that its a tank...

The original Drk in Final Fantasy was a tank.

Dark Knight's signature ability is Darkness, which consumes their HP to deal damage. Cecil was only a tank after he became a paladin.

It was a damage dealer in IV, X-2, and XI, as well as Tactics and Legend/Dimensions. And the remake of III (it originally was called something else).

It actually hasn't been in very many games at all, but it was never a tank. Of course, single player games also rarely require true tanks, and the only one that ever has fit the bill is Paladin due to Cover and low HP auto-cover.