BOB

The BOB is a special type of enemy encountered in Halo: Reach. The BOBs usually take the form of yellow/gold-armored Sangheili Rangers. In the ONI: Sword Base level, BOBs take the form of a white-armored Elite with randomly generated armor, ranging from Minor to Field Marshall. These white-armored BOBs always dual-wield Plasma Rifles, regardless of rank.

Description
Killing one of BOB's will reward the player the "Seek and Destroy" medal. However, the medal can only be viewed on Bungie.net. In the post-game carnage report, the BOB is referred to as an "Elite light vehicle". On Bungie.net, their description is simply "Wipe them out."

The name "BOB" is a reference to Bungie's Marathon video game series. In the series, all of the encountered human characters, besides the player, are known as "BOBs". "BOB" is an acronym for "Born on Board", a reference to the characters having been born onboard the titular colony ship. The AI Leela instructed the player to save as many as possible, but Bungie encourages the player on secret terminals to kill them all. The Vidmaster's Challenge states that the player must "Never, ever leave a single BOB alive."

BOBs are considered easter eggs, and thus have no canonical explanation in the Halo story.

BOB locations
Basic multiplayer map knowledge is helpful to finding some BOBs

Winter Contingency
The BOB can be found near the middle of the level, located on the riverbank across from the buildings with the second truck.The time it appears and disappears is currently unknown.

ONI: Sword Base
This BOB is very mysterious as it is not the typical golden ranger class, instead it is white and can be any Elite class. In some rare cases, it will be a Ranger. It can be found outside Sword Base in the spot you start the mission at the second time you enter the area. If it is not there it will be inside Sword Base in the same room as the shotgun spawns in multiplayer, below the damaged area where one would get to the area with the Spec Ops Elites.

Nightfall

 * When you get to the section where you assist the local militia there will be a BOB walking on top of the buildings, this will also happens on the "I'll Just Leave This Here" chapter.
 * Another one is occasionally spotted on top of one of the buildings in the beginning of the level, where you first go sniping.
 * Yet another one can be spotted mong some Jackals around the area where the platform where you battle the Hunters is located.

Tip of the Spear

 * As you head for the first AA gun, there will be a hill to the left, a BOB will sometimes spawn there.
 * After your Falcon crashes the BOB is found nearby the first bravo objective in Invasion on Spire, he is wielding a Fuel Rod Gun so he is very dangerous, especially on higher difficulties.
 * Another one on this level will occasionally spawn, again with a Fuel Rod Gun, among the Skirmishers and Grunts. Note that if this one spawns, the one above will not.

Long Night of Solace

 * At the beginning of the level when securing the beach, wait for three deployments to occur. After that, A BOB will be deployed in a Drop Pod.
 * The BOB is located in the control room near the end of the level. More specifically, it is working on the terminal near the back of the room.
 * Another BOB also spawns when you have to defend the Pelican, it is on one of the platforms. If this one spawns, the one mentioned above will not.

Exodus

 * Note that this is unconfirmed, as if it is factual, the disappearance time is almost instant* During the first barrage of suicide Grunts, there is a Golden ranger Elite that can be briefly fought before disappearance. If it is factual, no one has been reported of killing him.

New Alexandria

 * Boosting in the map at a very low altitude on the ground, somewhat near the Club Errera area.

The Package

 * When the player enters the courtyard, instantly turn left. On the side of the bridge where the Bridge spawn is in firefight, the BOB will be there, escorted by 3 jackals. This BOB will only attack with melee and grenades. It is best to kill the jackals with a grenade before engaging the BOB., and, if skilled, the player can lure it down for Noble Team to take care of.
 * In the section of Sword Base with the Spec Ops Elites, dash past them and the General, and go through the door on the far right. In the room should be a BOB with an incrediby fast disappearance time. Be careful with him, as he is very clever.


 * In the battle outside of Halsey's lab, at the end, when a Phantom drops off a second Wraith at the end of the ice shelf, it will also drop off a lone BOB.

Pillar of Autumn
After getting through the first half of Boneyard, go up to the top level in between the two sides of Boneyard, grab the sniper located in the doorway on the right. The BOB is inside the garage across the way.

Lone Wolf
After fighting enough enemies (exact number unknown but would be very helpful to this section) a BOB will appear wielding an energy sword, he is the same color as all the General class elites attacking you, so he may go unnoticed. This BOB was likely placed to kill a player who has been playing on the level for too long, as BOBs are more powerful than standard elites.

Trivia

 * Each BOB has a set time limit before it vanishes. For some BOBs, this time frame begins as soon as it is alerted to the player's presence. For others, the countdown begins once the player enters a certain area, thus it is possible for the player to miss the BOB entirely if it is not spotted. Also, if you assassinate a BOB, it might disappear. If it does, you'll be assassinating air.
 * In Halo: Reach all ranks of Elites, even Elite Ultras, even though they're already white, can be BOB's.
 * In the level ONI: Sword Base, BOBs can be any elite armor variant.
 * On 1/19/11 Bungie revealed the location of a Gold Ranger-class Elite in the Challenge titled: "Golden Tree City" the description read: "Find and kill the Gold Ranger-class Elite in a Banshee, fast and low, while on New Alexandria, on Legendary". Whether or not he is a BOB is unknown, as even though all Gold Ranger-class Elites are BOB's, killing this specific enemy doesn't result in a Seek and Destroy medal, nor the mention of an "Elite Light Vehicle" in the carnage report, even though it fits with the classical description of a BOB, as he is in a very fast Banshee which avoids combat, and whose tail is permanently lit even when the vehicle isn't boosting making it look largely different than other Banshees. As he is in a driverless Banshee, there's no body seen when the Banshee is destroyed, so it is impossible to check if he is indeed a Gold Ranger-Class Elite. This, along with the fact that he gets killed while inside a vehicle, and not directly by the action of the player, could also explain the lack of an actual BOB kill, and its absence from the carnage report aswell as the lack of a Seek and Destroy medal. Still, this is the only Gold Ranger-class Elite known to be in New Alexandria, the only mission left where none were ever found is Exodus.