Yes Man

Yes Man is a securitron robot that serves as Benny's assistant in 2281, and is an integral part of Benny's scheme to take control of Vegas.

Background
Yes Man was originally a generic securitron robot working for House, like all the other securitrons found on the Strip. He was damaged by a pulse grenade, and was recovered by Benny, who then allowed a member of the Followers of the Apocalypse to examine the securitron, in exchange for reprogramming it.

The reprogramming was extensive, and resulted in Yes Man being designed to do exactly as he is told (although the lack of restrictions on who is doing the ordering would later be Benny's undoing). The plan was to somehow dispose of House, plant Yes Man's A.I. in the Lucky 38 mainframe which would then put him (and by extension, Benny) in control of all the other securitrons on the Strip, and then take the platinum chip to Fortification Hill where he could activate the securitron army, enable the Mark. II OS and use the upgraded securitron army to take control of Hoover Dam and Vegas.

Yes Man is left behind when Benny flees to the Fort after the Courier pursues him to the Tops, and is soon after found by the Courier.

Quests

 * 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 him or herself.
 * Wild Card: Change in Management: the Courier must obtain the platinum chip, assassinate House, and install Yes Man's A.I. in the Lucky 38 mainframe.
 * Wild Card: You and What Army?: the Courier must travel east of the Colorado to activate an army of securitrons locked away in a secret Vault.
 * Wild Card: Side Bets: the Courier must meet with the various factions of the Mojave and decide who will be spared in the upcoming battle.
 * Wild Card: Finishing Touches: the Courier must convince Julie Farkas to support an independent Vegas, (optionally) protect President Kimball against an assassination attempt and use an override on the El Dorado Substation in order to power the Lucky 38 and allow it to broadcast the securitron operating system upgrade.
 * 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.

Other interactions
After speaking to Yes Man, the Wild Card series of quests will begin. The player can choose to continue Benny's plans, and start the Wild Card: Change in Management quest. This quest chain leads to No Gods, No Masters, where the player will take control of the Dam and later, Vegas.

Appearances
Yes Man appears in Fallout: New Vegas.

Behind the Scenes

 * In English slang, a "yes man" is an obsequious and unquestioning assistant or underling.
 * Yes Man's personality change seems to be a remnant of a post-ending gameplay sequence as it is, writing-wise, awkward, and creates a pointless plot twist. Unless, however, post-ending gameplay were possible, in which case it would be necessary, otherwise the player would have complete control of Vegas which, from a development perspective, would be difficult if not impossible to handle.
 * As a side note, this twist also makes it possible to have the Yes Man as the "canon" ending, because if the player is the ruler of Vegas, it makes skirting around the details of the PC (name, etc.) difficult since he/she is such a public figure. If Yes Man takes control of Vegas with his more assertive attitude, this reduces the importance of the Courier and thus makes the independent ending possible as a canon ending while not making writing future games difficult. If the current speculation is correct in saying that the most popular Steam ending will be considered canon, this is a useful thing to have put in the game, from a writing perspective.