This is going to be great! I'm going to help you accomplish so much, whether I want to or not!
Yes Man is an AI program that serves as Benny's assistant in 2281. He is an integral part of Benny's scheme to take control of New Vegas. Yes Man appears to be a modified Securitron. More specifically, his personality program has been put into a PDQ-88b Securitron; although he may later assist the Courier in the "independent" New Vegas options for the game's ending as the Lucky 38's mainframe.
Yes Man was originally a generic Securitron robot programmed to work for Mr. House like all the other Securitrons found on The Strip. He was recovered by Benny and several of the Chairmen after being damaged by a pulse grenade. Following this incident, Followers of the Apocalypse member Emily Ortal examined the Securitron in order to learn Mr. House's secrets in exchange for reprogramming him for Benny's personal use.
The reprogramming was extensive and resulted in Yes Man being designed to do exactly as he is told; thus, Yes Man is not just the Robot's name, it's also its job description. The plan was to dispose of Mr. House and install Yes Man's A.I. onto the Lucky 38 mainframe, putting Yes Man (and by extension, Benny) in control of all the Securitrons on the Strip. The next step was to take the Platinum chip to The Fort, take control of the great weapon he suspected Mr. House of having hidden away (as he did not know exactly what was stored there), and use this "weapon" to assume control of New Vegas and Hoover Dam.
Yes Man is initially located in Benny's suite in The Tops casino. To gain access to Yes Man, the Courier must either kill Benny in the casino, sleep with him (needs Black Widow perk), or confront him and force him to flee to The Fort.
To find Yes Man, enter The Tops casino and proceed straight ahead past the casino floor to the elevator bank (near the sign that says "Elevators out of Order"). Take the second elevator on the right to the 13th floor. Exit the elevator, turn right, and enter the third set of doors on the left side of the corridor (double doors with potted trees flanking them). Go into the room and through the hole in the wall in the back of the room.
After the player finishes Ring-a-Ding-Ding!, Yes Man will have moved to the front of The Tops casino in order to begin communication and further mission progress with the Courier.
Wild Card: Ace in the Hole: The Courier meets Yes Man for the first time. As there is no restriction on who Yes Man can help, the Courier can interrogate him to find all the details of Benny's plan, and even continue it themselves.
No Gods, No Masters: The Courier must power up the secret Vault, allowing the Securitrons within to break out and crush the Legion, before convincing the NCR to leave the Dam to Vegas - by force, if necessary.
After the assault on Hoover Dam, Yes Man informs you that he has found pieces of code within Mr. House's mainframe that will "change his personality", and that he will seem to be offline for a little while until his personality change is complete. This personality change makes him more assertive, meaning that he will take orders only from the Courier in the future.
The Courier, with the aid of Yes Man, drove both the Legion and the NCR from Hoover Dam, securing New Vegas' independence from both factions. With Mr. House out of the picture, the remaining Securitrons on The Strip were hard-pressed to keep order. Anarchy ruled the streets. When the fires died, New Vegas remained, assuming its position as an independent power in the Mojave.
The Courier, with the aid of Yes Man, drove both the Legion and the NCR from Hoover Dam, securing New Vegas' independence from both factions. With Mr. House out of the picture, part of the Securitron army was diverted to The Strip to keep order. Any chaos on the streets was ended, quickly. Chaos became uncertainty, then acceptance, with minimal loss of life. New Vegas assumed its position as an independent power in the Mojave.
Although Yes Man may appear completely joyous, there is evidence to suggest that he has emotions, For example, it is clear that Yes Man hates the Great Khans, though is only able to convey this on a passive-aggressive level, by calling them "dirty people" and hoping they will get wiped out by radscorpions after the Courier convinces them to leave New Vegas.
Yes Man becomes hostile briefly when attacked. His personality is distributed across all Securitrons, so he can't be permanently destroyed.
Yes Man will comment if he is attacked, his body is destroyed, or if he witnesses the Courier killing anyone.
If the player is female and seduces and kills Benny with the Black Widow perk, Yes Man will remain in the back room of Benny's suite instead of moving in front of The Tops casino entrance.
In the French version of the game, Yes Man is called "Béni oui-oui" ("Béni" is French for "blessed" and "oui" meaning "Yes"), a slang term given to a person who always agrees with the authorities.
Regardless of what the player does, the Yes Man questline will always be available. This means that if all other avenues of completion are impossible (due to faction reputation, etc), the game can still be finished.
Yes Man is the only named Securitron that does not disappear or become disabled after Mr. House's death.
True to his name, he will agree with everything that the player says, except when he/she tells him that he/she is the Courier that Benny shot.
Yes Man will re-spawn if killed in Benny's suite.
Yes Man is not affected by the Mark II software.
It is possible to melt or disintegrate Yes Man, making any further gameplay with him impossible, as disintegrated enemies do not respawn. Oddly, when this happens, any quests he is associated with do not end or fail. This is possibly due to the game being set to immediately respawn him.
Since Yes Man cannot die, unless disintegrated, killing him will give the player a seemingly infinite supply of scrap metal.
"And if you had, you know, a huge killer robot at your command, yeah, that would just clutter things up; and a lesser person might want that kind of overwhelming force on their side, but you know - where's the challenge in that?"