Hell Knight/Doom 3

The Hell Knight in Doom 3 is very muscular and heavy. An in-game examination of their spine indicates they have massive skeletons as well. They have no visible eyes, ears or nose. Their attacks are very similar to the Imp: melee attacks (including biting) and aquamarine fireballs with splash damage. When facing one of them, it is strongly recommended to use the Soul Cube or the BFG, for they can absorb large amounts of damage.

The first Hell Knight's appearance was in Delta Labs 4. Two of them appear in a relatively open room where a portal opens and 2 Hell Knights come from. This might be a reference to the first bosses in the original Doom, where the player must defeat a pair of Barons of Hell at the end of Knee-Deep in the Dead.