Jiralhanae Stalker

The Stalker is a Brute (Jiralhanae) rank.

These Special Police Units are feared by all factions.

Stalkers are covered in grey armor, and possess integrated circuitry for Active Camo in their Power Armor. They often use Radar Jammers to confuse their prey, and are the main users of Incendiary Grenades and Brute Plasma Rifles.

Apperance
The Brute Stalker nether appears in Halo 2 and only two levels of Halo 3 The Ark (Level} and the The Covenant (Level}.

also of note the Majority of the Brutes that appear in the interactive Believe Memorial on Halo 3.com wear the Stalker armour althrough one of them is persifically classified by the UNSC as a Minor.