The two major sides in the war are the humans and the Covenant. The Covenant is an alliance of several races, several of which appear in the game. The Halo itself is inhabited, and we will encounter native life, both friendly and hostile. Because spoilers are enabled, each entry contains additional tips for interacting (violently or otherwise) with these characters.

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	The Master Chief: You play a cybernetically enhanced soldier, clad in a high-tech battlesuit. As this elite warrior, you travel the Halo fighting alongside the other humans and trying to stop the Covenant from seizing its secrets; you are the only SPARTAN supersoldier on the planet. The image visible on his visor may sometimes look like a face but it's just a "gleam" effect; the visor is opaque. Offense: Play your best and prevail. Defense: Ditto.
	Marines:These are the rest of the human forces on the Halo, normal non-enhanced troops. There are many ways for them to vary their appearance, showing off Halo's modeling system. The name "Bobs" was given to them early on by fans since they seemed to serve a function similar to that of the Bobs in Marathon 2 and Marathon Infinity; they are officially referred to as Marines. In the game they will accompany you and assist you, with AI sophisticated enough to run the Jeep's mounted gun or call out orders to each other. Offense: Use the marines as bait while you flank the enemy, or vice versa. When driving vehicles that allow it, let the marines hop on board. They greatly improve your firepower. Defense: Don't get between the marines and the target. They're only human. If you kill too many marines, accidentally or otherwise, you will be branded as a lunatic/traitor and terminated on sight. Be mindful of friendly fire, both at and from you.
	Crew: This is one of the crew of the Pillar of Autumn, assisting the Chief in his re-activation. Offense: These guys aren't as well-armed or trained as the marines, but they can put up a good fight with their pistols. Defense: They aren't as brave as the marines either, so they retreat and panic easier.
	Covenant Elite: These large fighters are the main species of the Covenant. They seem about eight feet tall, with a few more leg joints than humans have, and they wear shining armor. They are also equipped with personal forcefields. Offense: Elite shields are more vulernable to plasma weapons, while their armor is more vulnerable to bullets and melee attacks. Use the appropriate weapon for the condition of the Elite you are facing. If an Elite is near death, he will sometimes go bezerk, roar, and charge you. Elites have a powerful melee attack. Watch out if they get close to you. Defense: Elites usually wield Plasma Rifles or Needlers. Elites are bold, but they aren't stupid. Lay down suppressing fire or grenades to make them take cover, and use that to give yourself some time to reload or recharge your shields. Late in the game, the black Spec Ops Elites will appear. These are quite powerful, but not as dangerous as the Yellow Commanders.
	Commander: Elites wearing yellow armor are significantly stronger than the other types. They also have a fondness for powerful energy swords. Fear them. Offense: Commanders have very powerful shields, but underneath they aren't much tougher than normal Elites. Take down their shields with plasma weapons and they're easy(-er) prey. Two surefire ways to kill a Commander: Stick a plasma grenade on him, or fill him with an entire clip from the Needler. Either is guaranteed to kill him, but if he charges you will get caught in the blast. Defense: Throwing grenades, even if you don't damage a Commander, will make him dive for cover, giving you a few extra seconds. Run.
	Invisible Elites: Some Covenant warriors have been issued cloaking devices, an effect which must be seen in motion to be believed (try the Tokyo Game Show 2001 movie). The Covenant here is on the right side of the image. Offense: Bullet weapons, especially the assault rifle, will disrupt their cloaking device and make them momentarily visible. Cloaked Elites don't have forcefields, so they take much less damage. Don't be afraid to charge in for the kill (once you know where he is of course). Don't bother using the Needler, the needles do not track cloaked Elites. Defense: Cloaked Elites with energy swords tend to roar before charging. This gives you about a second to locate him and/or get in the first shot.
	Grunt: This alien is a race subservient to the Covenant, used as infantry. The equipment he wears is to provide an environment similar to his low-temperature home planet. They are dangerous in packs, but cowardly and easily startled, and tend to yap out hilarious dialogue in their squeaky voices. Offense: For long-range work, aim for the head with the pistol. Sometimes, you will come across Grunts sleeping on the job. They won't wake up if you don't fire your weapons, so kill as many as possible with melee attacks. Grunts with grenades stuck to them are quite unpredicatable, equally likely to run back to their friends, straight at you, or just fall to the floor wailing. Use this to your advantage. Defense: Grunts are easily frightened. Killing a nearby Elite is a good way to panic the whole crowd, making them flee (and stop firing). Grunts usually pack Plasma Pistols or Needlers, and on higher difficulties are issued plasma grenades. Late in the game, the black Spec Ops Grunts use Fuel Rod Guns similar to the ones used by Hunters. These guns explode after their owner is killed.
	Hunter:These walking tanks are the Covenant's heavy infantry. They are armed with a Fuel Rod Gun attached to their right arm, and a huge shield that can deflect just about anything. Offense: A Hunter's weak spots are the orange portions of his armor: Neck, back, and belly (usually covered by his shield). When a Hunter charges, he always swings his shield twice. If you dodge the first swing, you have a moment to let him run past you and fire at his exposed back. Defense: A greenish light emanating from a Hunter means that he's preparing to fire his gun. Hunters can fire several times in quick succession when angered. If a Hunter dives out of the way of a vehicle, his Fuel Rod Gun automatically powers down. Hunters appear as unusually large dots on the motion tracker, and their clanks can be heard from quite far off.
	Jackal: Another species of Covenant, these guys form an elite infantry (much stronger than Grunts, but not matching the powerhouse Elites). They carry a portable shield, which can deflect a large amount of firepower, and they are skilled at using it for defense. Jackals are almost always found in groups of four, and will cooperate to outmaneuver enemies. Offense: There is a small gap in a Jackal's shield for him to fire his weapon. Careful aiming can find it. A Jackal is well-protected only when he is standing still. It's hard for them to use their shield effectively while moving. Jackals don't pay much attention to grenades (on lower difficulties, at least). A fully charged shot from the Plasma Pistol will burn out a Jackal's shield, leaving him vulnerable. Work with your marines to attack from several directions. He can't block every shot. Defense: Often, one jackal will pin you down while another tries to flank you. Sometimes it's better to break cover and eat the damage than be attacked from multiple sides.
	Sentinel: These robots are 343 Guilty Spark's assistants/henchment/etc. They are armed with Forerunner energy beams and sometimes forcefields. Offense: Sentinels are extremely vulnerable to Covenant (energy) weapons. Often, you will encounter Sentinels fighting groups of other enemies. Let the two sides battle it out, then pick off any weakened survivors. Defense: As their name suggests, Sentinels tend to stay in one place and don't pursue their targets much. The Banshee is extremely vulnerable to Sentinel weapons. The Needler and plasma grenades are very effective against Sentinels.
	Flood Infection: These small creatures are the "real" form of the Flood, who burrow into their victims and transform them into Warriors. They give and take very little damage, but that's not much comfort when faced with dozens of them. See our Flood Anatomy section for more information. Offense: Infections do a small amount of damage when they burst, enough to set off other Infections around them. Entire swarms of them can be quickly destroyed by these chain reactions. If one gets close enough, it will launch itself at you. Time your melee attacks to knock them out of the air. Your energy shield completely blocks out Infections. Sometimes it's easier to just let them bounce off you and eat the tiny damage they do (don't forget that damage adds up!) Defense: When your shields are down, Infections gnaw at your armor and can do a great deal of damage. If your shields drop in a Flood battle, retreat immediately. Don't ever throw plasma grenades at Infections, they will keep right on coming and bring the grenade back at you.
	Flood Warrior (Covenant): These hapless Elites have been overwhelmed by Infections and transformed into shambling, deformed corpses that obey the Flood embedded in them. They are just as fast and strong as their proper form, however. See our Flood Anatomy section for more information. Offense: Warriors are usually too dumb to avoid nearby grenades. Don't bother with the melee attack, they will shrug it off and respond immediately in kind. Bullets work best on them, but they are virtually immune to the sniper rifle. Defense: Warriors use weapons scavenged from their victims, both human and Covenant. Warriors have decent aim, but they're terrible at tracking targets. Keep dodging. Don't stick a plasma grenade on a charging Warrior, he'll happily return it to you. Warriors have a nasty tendency to get back up after being beaten down, even if they've lost body parts.
	Flood Warrior (Human): Human marines, without energy shields, were easy prey to the Flood Infections. Now they have been forced back to life by the Flood to slaughter their former comrades. See our Flood Anatomy section for more information. Offense: Warriors are usually too dumb to avoid nearby grenades. Don't bother with the melee attack, they will shrug it off and respond immediately in kind. Bullets work best on them, but they are virtually immune to the sniper rifle. Defense: Warriors use weapons scavenged from their victims, both human and Covenant. Warriors have decent aim, but they're terrible at tracking targets. Keep dodging. Don't stick a plasma grenade on a charging Warrior, he'll happily return it to you. Warriors have a nasty tendency to get back up after being beaten down, even if they've lost body parts.
	Flood Carrier: Corpses deemed unfit for Warrior status are turned into breeding grounds. They waddle along on what's left of their legs until they take too much damage or find themselves near an enemy, and then burst with a powerful blast, releasing Infections to feast on nearby survivors. See our Flood Anatomy section for more information. Offense: It doesn't take much to set off a Carrier. Try to get them at as long a range as possible. When a Carrier is killed relatively cleanly, or voluntarily explodes as a weapon, it will fall to the ground pulsating before it goes off. However, a blast from the shotgun will cause it to explode instantly. This can be good or bad depending on who is nearby at the moment. Defense: A Carrier killed by a nearby explosion is often hurled into the air, landing some distance away before bursting. Beware of low-flying Carriers. A dead Carrier releases anywhere from three to six or more offspring (possibly dependent on difficulty). When fighting crowds of Carriers, watch out for the growing horde of Infections.