Sergeant Johnson

Summary
Sergeant Avery J. Johnson has been fighting the Covenant since he was old enough to join the Marines. After joining, he was assigned to the troop regiments on Paris IV. When the Covenant attacked the planet in the Siege of Paris IV, Sergeant Johnson fought valiantly. He captured a crate of plasma grenades from the Covenant when his troops needed weapons and used them all against the Covenant to keep them at bay so his troops could evacuate. After they returned to Reach for reassignment, doctors discovered an unusual side effect of using so many plasma grenades: a type of radiation poisoning called Boren's Syndrome had affected Sergeant Johnson's neural electric pathways. He refused treatment, and this ultimately helped him in the future.

After being assigned to the Pillar of Autumn and her secret mission, he took command of the Marines on board. He was instrumental in helping keep the Marines effective even after they were marooned on the ring-world Halo. He was presumed dead after Master Chief found a helmet recorder entry from PFC Wallace Jenkins that displayed a parasitic organism, The Flood, attack Sergeant Johnson, Captain Keyes, and PFC Jenkins. After he had been recovered alive with other surviving members of the Pillar of Autumn aboard a Pelican Dropship, it was discovered that the Sergeant's medical condition was the cause for his survival, because the Flood could not force a match between it's neural pathways, and that of Sergeant Johnson's. He is currently still alive and on active duty.

Halo 2
In Halo 2, he is promoted to Sergeant Major and given the Colonial Cross by Lord Hood for his efforts.

On Cairo Station, he aids in the defence of the station by setting up a stationary turret. When the Master Chief goes down to the Outskirts of New Mombasa to combat the Covenant there, Sergeant Johnson carries a Sniper Rifle for use, but leaves after the encounter with Hunters. He reappears in the ending cutscene of Quarantine Zone, where he futilely attempts to stop the Arbiter. He breaks free of Tartarus' captivity and later aids the Arbiter in stopping Tartarus from activating the Halos by blasting open the door to the control room with a Scarab, and then shooting off Tartarus' energy shield with his Beam Rifle, enabling the Brute chieftain to be taken down.

In all his combat appearances, Johnson cannot be hurt by any weapon available, even the Banshee's Fuel Rod Cannon.

Quotes
From cinematics and gameplay:

"I know I'm pretty, but we've gotta get to work!" "Hey bastards, knock knock!"

"Back when I joined the Corps, we didn't have any fancy-shmancy tanks, we had sticks...two sticks and a rock. And we had to share the rock."

"Usually the Lord works in mysterious ways, but not today. This here is 66 tons of straight up, HE spewing, divine intervention! If God is love, then you can call me Cupid!"

"Dear humanity, we regret being alien bastards, we regret comin' to Earth, and we most definitely regret that the Corps just blew up our raggedy-ass fleet!"

"Do I look like an 8-foot-tall blue alien monster to you?"

"Oh, I know what the ladies like." (after delivering a tank to Cortana, who complains that the Master Chief "never gets me anything")

"Get tactical, Marines!"

"Dammit, Jenkins, fire your weapon! Don't even think about it, Marine."

"Boy, you always got a bad feeling about somethin'."

"Hey, mohawk! How's that feel?" (as he shoots Tartarus) "For a brick, he flew pretty good!"

"Well, I don't care if [Halo] is God's own anti-son-of-a-bitch machine or a giant Hula Hoop--we ain't gonna let 'em have it! What we WILL let 'em have is a belly full of lead and a pool of their own blood to drown in!" "Hey, don't shake the light bulb."

"Would it help if I said please?"

"All you greenhorns who wanted to see Covenant up close, this is gonna be your lucky day!"

"Listen up! You had the chance to be afraid before you joined my beloved Corps! But to guide you back to the true path, I've brought along this motivational device!" (indicates Scorpion tank) "Our big green style cannot be defeated!"

"I heard that, jackass!" (over the intercom, to a marine who says, "Dear Sarge, having a lovely time kicking ass in outer space. Wish you were here!") "Would you MIND not killin' my men?!" (when you run over a marine with a vehicle)