Rex (Fallout: New Vegas)

Rex (full designation of Cyber-Hound Mk. III, LEO Support Model, Serial Number B955883) is a 209 year old cyberdog living in Freeside in 2281. He is owned by the King. He hates rats and will immediately go for one if he sees one. He also doesn't like hats, or people who wear them, and it's unknown why, although the King says it might be because "hat" rhymes with "rat."

Background
Rex is a cybernetic dog that has been around since pre-War times. He was used by the Denver Police Department. Since then, he's been the loyal pet of The King in Freeside. He may have once been owned by Caesar, as Antony notes to the Courier that he (Caesar) used to own a cyberdog. Also, there are red bulls painted on Rex's sides that are identical to the Caesar's Legion standard. Capable of sniffing out loot and taking a large amount of punishment, he will join the Courier during the quest Nothin' But a Hound Dog. If the quest is completed, Rex can become a permanent Companion.

Four different dog brains can be used to complete the quest Nothin' But a Hound Dog. They are:
 * Lupa's Brain from The Fort, which increases Rex's health from 450 to 550
 * Rey's Brain, which increases Rex's Attack
 * An NCR Guard dog brain, which grants no additional effect
 * Violetta's Brain (from the quest Three-Card Bounty), which increases Rex's speed

Interactions with the player character
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Appearances
Rex appears in Fallout: New Vegas.

Bugs

 * If you dismiss Rex during "Nothin' but a Hound Dog", when he is theoretically on loan to you and not a permanent companion, he may disappear and not return to The King. He eventually showed up after I traveled to Doc Henry and was told that I needed the dog to perform the surgery. (Was hoping he'd reappear as a completely different entity similar to ED-E's upgrade process).


 * When you tell Rex to wait at the Lucky 38, he can sometimes dissapear and not be found in any of the rooms at the Lucky 38 he will be with the king once you find him he will bee-line to the 38


 * After replacing Rex's brain, he may become immobile.


 * After replacing Rex's brain with Lupa's, his health is reset to 100/0 (440/440 is default). Rex gets knocked out after one hit. There is an easy fix for this, bring up the console with the ~ key, click on Rex, then type in "Kill" After Rex dies, bring up the console again, click on Rex, then type "Resurrect" and Rex will come back to life with his health reset to 440/440.


 * When asked to wait, Rex may disappear after the player leaves the area. Npcs will still make remarks to you as if he was there.This can be fixed by waiting 3-5 days.If this happens during "Nothin but a Hound Dog" you will have to wait to be able to finish Guess Who I Saw Today, if Rex is not returned by the time Lily needs to be tested and you have gotten a brain, Lily will not be tested until Rex receives his new brain.


 * Currently, Rex has a bugged dialogue-script at the end of "Nothin' but a Hound Dog". After his brain is transplanted, Rex will come forward to you and the game will freeze. (Confirmed; resolution unsure. More detail required.)


 * After replacing Rex's brain with Lupa's, his health was set to 540/440 (440/440 being the default). Upon taking damage that reduced his health beneath 440, it could not be restored past 440. This obviously made Lupa's brain's "Blood of the Legion" perk effectively useless.


 * If Rex is with you when you talk to Corporal Sterling in Camp McCarran then he will attack the First Recon group. This is either a bug or due to his dislike of hats.


 * During combat, Rex might chaotically run around from-and-to foes while not attack.


 * When knocked unconscious by the Courier, at times Rex will be randomly shoot hundreds of feet into the air (Similar to a grenade going off).


 * After Rex joins you, he will sometimes refuse to attack regardless of what state or setting you choose for him. He will continue to remain passive throughout the game.  There is an easy fix for this, bring up the console with the ~ key, click on Rex, then type in "Kill"  After Rex dies, bring up the console again, click on Rex, then type "Resurrect" and Rex will come back to life able to attack things again.


 * If Rex is told to wait for you at the Lucky 38 he may not be found there when you return but he might be found back with the king and when approached will start running back to the Lucky 38


 * Rex might sometimes not follow when fast traveling. He will be waiting on the spot you traveled from. He will still be in your party and will follow you if you select "follow" through the companion wheel. Other times he will stay put after a fast travel. Selecting "stay" then "follow" will make him follow you again.--Needs confirmation.


 * Rex will sometimes wait without being told to, this can be fixed by telling him to wait, then tell him follow you again.


 * If you talk to Rex as soon as you get him for Nothin' But a Hound Dog, and the Perk for having him with you pops up, you will enter chat with him, but will have no options to talk. (Screen zooms in, he turns towards you, and no chat options appear.)


 * If you separate from Rex and tell him to go to the King, the pop-up message will tell that Veronica went to lucky 38 (In the French PAL version at least)