The Ice Climbers, known in Japan as Ice Climber, (アイス クライマー, Aisu Kuraimā) are the pair of playable protagonists from the game Ice Climber, released in the pre-Super Mario Bros. era of NES games. When playing a one player game, the player plays as Popo. When playing a two-player game in Ice Climber, player one plays as Popo, while player two plays as Nana. In both Melee and Brawl, certain color changes will make Nana the leading, player-controlled climber.
Despite not being displayed, the CPU-controlled Ice Climber in the Smash Bros. series does indeed have his or her own separate percentage or stamina counter. This alone results in the Ice Climbers' extremely high learning curve for both Smash Bros. games that they have appeared in, as players must ensure the safety of not one, but two characters at the same time. The payoff can be highly rewarding, however; they are placed near the top of most accepted tier lists.
Both of the Ice Climbers are small, young children. They both wield wooden mallets, which they use to whack enemies and break ice cubes. Both of them wear parkas; Popo's parka is blue while Nana's is pink. They can also be identified by the patch of hair exposed from their hoods.
The relationship between Popo and Nana is unknown and was not elaborated on in Ice Climber. As the two are said to be "rarely seen apart" in Melee, among the ideas thought up of by fans are that the two are siblings, friends, or even lovers. According to Nintendo, the nature of their relationship is up to the player's imagination; as a result, no hints to their relationship has been directly stated in any media. Melee offers some insight to the potential relationship to the two; a brief shot in the Opening of Melee features Nana and Popo high-fiving each other, with a small heart coming out from where their hands meet, and the Japanese title of Event 21: Ice Breaker roughly translating to "Be the jammer of their romance".
The Ice Climbers made their debut appearance in the Super Smash Bros. series as a dual-controlled pair of fighters. They (as a singular entity) are one of the 14 (15 if Sheik is counted) default characters available from the start of the game. They are ranked 8th on the tier list, in the S tier.
The Ice Climbers still consist of Popo and Nana. They still fight as a pair with Nana following along. With Nana by the player's side, special moves in particular are better than just being Popo. Both Ice Climbers can now hang on a ledge at the same time and their down-special in the air is no longer an auto-freeze. The Ice Climbers' Final Smash, Iceberg, consists of a large iceberg taking up a large portion of the screen. It deals damage to, and eventually freezes, those on or near it. The character can switch between Popo or Nana as the leader of the duo based on which color of costume is chosen. The threat of the Ice Climbers' 0-death chain grabs puts them in 2nd on the Brawl tier list in S tier only behind Meta Knight.
The Ice Climbers do not return as playable characters for Super Smash Bros. 4, though they do make a cameo as a collectable trophy. In a column for the Japanese gaming magazine Famitsu, Sakurai claimed that technical limitations of the Nintendo 3DS prevented their inclusion; the two were reportedly difficult to implement on the console, and as the duo lacked the potential for a new game in their debut series, Sakurai intentionally gave the Ice Climbers a low priority on returning. While they were fully-functional on the Wii U, Sakurai decided to cut the characters in order to keep the playable roster between the games identical.
 Crowd chants for the Ice Climbers, however, can still be found in the game. Because of a bug in the Japanese version, when the crowd is cheering for a Villager who is fighting Dr. Mario, they will instead cheer for the Ice Climbers.