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 ears or nose, and their eyes are very small and difficult to spot (they're on either side of the head, just above the mouth). 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.

In Hell, Hell Knights show a different appearance than those in Mars. Their skin is greyish green. Parts like mouth, upper chest, hands and feet are red (possibly from the blood of their victims). They also have several scars along their body with a particular one in the forehead shaped like a pentacle.

Combat Characteristics
The Hell Knight's attacks are similar to those of the Imp: melee attacks, but including biting, and energy balls with splash damage. The Hell Knight, however, doesn't have any sudden leaps and its energy balls have a wider area of effect, making them more dangerous in closed space, though they are easier to dodge as the Hell Knight's height means they are launched from farther up, making it possible to literally run under them. 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, and roughly as tough as the original Baron; the Doom 3 Hell Knight takes six direct rocket hits to kill, while the old Baron usually took five or six rockets (depending on the random damage rolls). It is probably for this reason that there is no Baron of Hell in Doom 3; the Hell Knight fills the role.

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 energy ball 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. A portal in a large room opens, and two Hell Knights emerge. 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.