Who's Who is a Perk-a-Cola in Call of Duty: Black Ops II in the Zombies game mode, first introduced in Die Rise. It costs 2000 points. The perk allows players to revive themselves after they are downed. If downed, the player will take control of a doppelganger that can be used to revive the player's downed character or any other downed player in the match. If players successfully revive themselves or if another player revives them, they will keep all perks and equipment they had before they got downed apart from Who's Who. The color of the perk is dark blue(sometimes seen as teal or turquoise), and the icon is two hands reaching for each other.
If the player does not revive themselves before they bleed out but is still alive as the doppelganger, they will become the doppelganger but will lose all perks and equipment leaving them with only the M1911. Perks and weapons can be bought while playing as the doppelganger. The double will spawn close to, but not near enough to see the player's body and will only have a M1911. If both the original player as well as the clone are down simultaneously, then their teammates will need to revive both in order to revive the downed player. In solo mode however, being downed as the doppelganger counts as the death of a player, thus ending the game. In case of the player's body being killed in an action such as falling down an elevator shaft or off the map, the player will respawn again in the default spawn room with no perks and the M1911, maintaining their points.
In Call of Duty: Black Ops Cold War, while not physically in the game, the perk's attributes are combined with Tombstone Soda which turns the player into a shadow in the Dark Aether armed with their weapons when downed, allowing the player to revive themselves.
Die Rise - in one of two elevator shafts once the power is turned on. Either the shaft down the hall from the initial spawning area, or in another down below. The location varies between games and the machine shares the spawning points with the perk machine for Speed Cola.
The appearance of the Who's Who Perk-a-Cola machine resembles a figure similar to a body, possibly relating to the secondary organism that is created when the Perk is used. It also has a Life Preserver around it, possibly due to the fact that the perk is mainly used to revive the original player. It also has a strange orb on top of the machine, with a hologram of a man reaching his arm out.
- Who's who can be used to earn "free" points with the Bank: After obtaining a large amount of points, the player has to get downed near the bank. Once controlling the doppelgänger, the player has to deposit the points in the bank, and then revive the player's body. Doing so will restore the points the player had to the initial amount, but keep the deposited money in the bank, which essentially duplicates the amount of of points used in the process.
- This is one of two methods that can be used to double the points in the Bank and fill it to the maximum. The second method uses the Time Bomb instead Who's Who.
- If the clone is facing the player, the crosshairs will turn blue
- When the clone is in action, all buildable parts will glow.
- After getting revived by the doppelgänger, the player will lose their Monkey Bombs.
- Despite the fact that all equipment is lost upon controlling the clone, including weapons, upon being downed and in the revival mode, Claymores are still able to be used.
- Who's Who will affect the solo version of Quick Revive, meaning if the player has both Quick Revive and Who's Who when they are downed, they will spawn as the clone, and after a while, Quick Revive kicks in and revives the player. This means that obtaining Random Perk Bottles in solo mode in Die Rise in an effort to obtain more than four perks is potentially dangerous because obtaining Who's Who will cancel out Quick Revive.
- It is possible to get another of the same gun with Who's Who.
- If a dead player spectates someone using a Who's Who clone, that player will hear "Who's Who!" for the rest of the game, as if using Who's Who.
- All points spent in Revival Mode will be refunded if the player revives themselves.
- If a Who's Who clone drinks Who's Who, the downed character will die and the doppelgänger will replace the character.
- Game files refer to Who's Who as "chugabud".
- In the song's jingle, towards the end, one can hear the singer cough, and a siren can also be heard.
- Who's Who was supposed to appear in Mob of the Dead and Origins.
- The backing track used for the Who's Who jingle comes from a stock track entitled "Rockabilly Kitty". 
- The Season 2 challenge for Call of Duty: Black Ops Cold War requiring players to revive themselves 10 times with Tombstone Soda is named "Who's Who?", referencing the combination of the two perks' abilities.
- I'm My Own Best Friend (10 / Bronze Trophy ) - In Die Rise, revive yourself.