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. It looks rather different from the old Hell Knight, as it doesn't have any horns, hooves and doesn't look anything like a goat, but its overall body structure is similar, albeit a bit more powerful.

Combat Characteristics
The Hell Knight's attacks are similar to those of the Imp: melee attacks, but including biting, and aquamarine fireballs with splash damage. The Hell Knight, however, doesn't have any sudden leaps and its fireballs have a wider area of effect, making them more dangerous in closed space. The Doom 3 Hell Knight is actually a mixture of the original Hell Knight and the Classic Baron of Hell, being tougher than the original Hell Knight, but a little weaker than the old Baron (It takes between four to five direct rocket hits to kill it). It is possibly for this reason that there is no Baron of Hell in Doom 3.

Tactical Analysis
When facing a Hell Knight, it is strongly recommended to use the Soul Cube or the BFG if it is necessary to take them down quickly, for they can absorb large amounts of damage. But if the situation permits, the Rocket Launcher, plasma gun, chaingun and even the shotgun are effective enough. It is a very bad idea to retreat from one when he's about to throw a fireball as its splash damage radius is rather large and it is recommended to avoid being in close proximity to walls or other solid objects. The chainsaw, while powerful, is not a good choice against a Hell Knight.

Trivia
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 emerge from it. 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. These two Hell Knights are tougher than those encountered later in the game, able to survive a fully charged BFG blast.