Hunters

From Halo - Wiki on Neoseeker

from Halo 2, and Halo 3.

Hunters are different from your avarage Covenant species, instead of a single enity these heavily armoured beasts consist of millions of worm-like organisms that are united under a single consciousness, and will always attack in pairs. Hunters commonly wear impenetrable armour made from an unknown alloy. Their main weapon is an integrated Fuel Rod Cannon that fires mortar-style green coloured plasma against ground troops and heavily armoured UNSC vehicles. Their plasma attack takes a moment to charge, and has splash damage. At close range Hunters will opt to use melee attacks instead of its powerful weapon, wielding their huge shields to smash their enemies - their Melee attacks are powerful and allow them to remove vehicles and objects from their path. Unlike nearly all other Covenant, Hunters cannot talk, and but have a distinctive whooshing sound when they fire their primary weapon.

There is an interesting section of Halo 2 where two Hunters escort you through a level. You will also fight alongside Hunters that you free from a Brig. This collaboration is possible because Hunters join on the site of the Elites in the Covenant civil war.

Strategies

When confronted by a Hunter, one of the most effective techniques is sniping. A few well aimed shots to the head can take down a Hunter in 4 or 5 shots. Sticky grenades and close range weapons to it's vulnerable back also take down these massive foes.
Using a Brute Shot and sticky grenades is also an effective way of taking down a Hunter

Halo 3 Hunter Strategies

In Halo 3 Hunters are once again on the opposing side, however, this time, if you plan carefully Hunters are VERY simple to deal with even in Heroic difficulty. In two of the locations where you are faced with Hunters you will probably have weapons that are superbly effective against them:

Tanks - Tanks can kill Hunters in a single shot.
Plasma Cannon - Plasma Cannon at close range will wreak havoc on Hunters. In Heroic you can easily take down 2 Hunters using only 50 rounds from a Plasma Cannon.
Gravity Hammer - the Gravity Hammer is slow, but very powerful. Against regular Brutes and other common enemies it is completely wasted. Instead, save it for use against Hunters and Brute Chieftains. Equipped with a Gravity Hammer you should be able to take out a Hunter in 2 strikes, depending on how injured the Hunter is from other weapons.