Geth Prime

Mass Effect
Standing twelve feet high and boasting the deadliest arsenal of any geth infantry, a Geth Prime is a terrifying opponent. They are instantly recognizable by their white armor and huge stature. Primes carry a pulse rifle - which can also launch rockets - have six levels of shielding and are incredibly resilient. They also boost nearby geth combat stats; it is this ability that sets them apart from the Geth Juggernaut. Primes have no major weaknesses and are resistant to biotic and tech talents. They are the largest bi-pedal geth unit, towering over the second largest unit, the Geth Juggernaut.

Tactics
The Geth Prime is used as not only a morale booster for other geth in combat, but also as an elite soldier. They are put into action where the geth need extra armor and firepower. Geth Primes have the Combat VI ability which boosts the combat prowess of all nearby geth, resulting in a faster rate of fire, better accuracy and more damage. Consequently it is a good idea to take out Geth Primes first before focusing on smaller geth.

Mass Effect 2
In Mass Effect 2, Geth Primes are armed with light machine guns and combat drones. They are one of the most dangerous synthetic foes in the game, next to the Geth Colossus and YMIR Mechs.

Capabilities
Offensive

Geth Prime do not seek cover and will generally attempt to engage at point-blank range. There is an exception on Haestrom where a Geth Prime will prefer to stay under the cover of the Geth Recon Drones. They are armed with the M-76 Revenant light machine gun, which they fire in long bursts, and they can melee you with it if you get close. They also have the ability to boost stats of nearby geth, jam your radar, fire siege pulses and can also deploy Combat Drones.

Defensive

Geth Primes have high shields, armor and health but do not seek cover.

Tactics

 * Disruptor Ammo and Armor Piercing Ammo, if available, are very effective against their shields and armor, respectively (both possess bonus health damage also). Warp Ammo is effective against their armor and health, and the damage is doubled against enemies being affected by biotic powers. Switching squad weapons to those with the greatest penetration power for that particular defense can augment your ability to damage their defenses even further. These can all be important when fighting Primes, as they possess powerful shields and armor. Seeking cover when fighting them would be wise.
 * Geth Primes tend to close in on Shepard and other squad members, walking around any cover while attacking. It is prudent that the group keep their distance when engaging them. If the Prime gets into point-blank range it can launch melee attacks in the same manner as Shepard.
 * Powers that are useful against their defenses include Overload, Warp and Explosive Combat Drone (distraction allowing free shots at them with low risk, and extra damage when the drone is destroyed). Tactical Cloak can be used if the player can seek separate cover from their squadmates to "ping-pong" the Prime back and forth. AI Hacking can also be very useful as the Prime will quickly eradicate lesser geth units in the area while at the same time taking some damage. While the Prime is under the effect of AI Hacking, either open fire on the Prime, possibly taking it out before the duration ends, or kill off as many other geth troops in the meantime, possibly leaving it alone when the duration ends. Or use the time to pull back and find some new cover. The Prime will not use Combat Drone or Morale Boost while under the effects of AI Hacking.
 * As noted above, Geth Primes will jam your radar, and are one of the only enemies in ME2 which do this. An observant player can take advantage of this by interpreting a jammed radar as an early warning that a Prime is nearby, before they've made visual contact.

Mass Effect 3
The Geth Prime will also be an enemy in Mass Effect 3. "Geth primes are command-and-control units that pulverize their enemies with pulse cannons, missile drones, and gun turrets." The Primes have been redesigned to have three eyes instead of one.

Capabilities
Offensive

As described, the Geth Prime has converted to more of a mobile command platform for the geth and is arguably more dangerous than before. It deploys combat drones and turrets (the ones the player can use rather than the ones Combat Engineers deploy) and wields a lethal semi automatic Pulse Cannon that can drop shields in one or two hits. These cannons also briefly stun you (roughly 1 second), so if you get hit once, you will probably take a second hit.

Defensive

Primes appear to have had an upgrade to their defenses, and are extremely dangerous without upgraded weapons due to their damage resistance. Primes have strong shielding and heavy armour. They are immune to biotic attacks such as Pull and Throw.

Tactics

 * Cover is a necessity. High-damage attacks such as Warp are effective, but they do not lift easily so a biotic combo explosion can be a challenge to set up.
 * It is possible to use sabotage on a Geth Prime, even at full shields and armor. This also converts any combat drone it has deployed, but not deployed turrets. This gains both a temporary, deadly ally while giving the player the opportunity to focus on other enemies or to wear down the Prime itself.
 * Headshots from high damage sniper rifles such as the Black Widow are very effective against their armor.

Trivia

 * Geth Prime units on the Pinnacle Station subterranean survival mode are equipped with a large, bluish-glowing version of the Pulse Rifle, which functions in the same manner as the normal Pulse Rifle.