Imperius, the Angel of Courage.

The current ruler of Heaven (who was still injured at the end of Act 4 and was taken over by Tyrael, the Angel of Justice).

It is one of the five archangels and represents courage.

Tyriel represents justice.

Israel represents destiny (visible in Act 4).

Auriel represents hope (visible in Act 4).

Mather represents wisdom (incarnated as the Angel of Death in the fifth act, the final boss).

The high-level heaven is controlled by these five archangels, and the Angel of Courage is the boss.