Raiden (Japanese: 雷電), real name Jack (ジャック, Jakku), is a fictional character and one of the protagonists of Konami's Metal Gear series. Created by Hideo Kojima and designed by Yoji Shinkawa, Raiden was introduced in the series as the main player character of the 2001 game Metal Gear Solid 2: Sons of Liberty. In Metal Gear Solid 2, he appears to be a member of the U.S. special operations unit FOXHOUND and is participating in his first mission against terrorists. Despite coming across as a young rookie, he is later revealed to have been a child soldier in his native Liberia, having earned the nickname "Jack the Ripper" (ジャック・ザ・リッパー, Jakku za Rippā). Raiden also appears as a supporting character in the 2008 game Metal Gear Solid 4: Guns of the Patriots, in which he is assisting the series' main protagonist Solid Snake in his fight against Revolver Ocelot's forces. He is also the main character of the 2013 game Metal Gear Rising: Revengeance, in which he is dealing with his past and his present life as a combatant who faces enemies from private military companies.

Raiden, who was inspired by the Sherlock Holmes stories and a fan's letter wanting a younger character to be featured in the series, originated from Kojima's desire to see Snake from a different point of view. His inclusion in Metal Gear Solid 2 was kept secret from gamers before his debut; despite some players' reactions, the staff liked the character. To appeal to fans of the series who initially disliked him, the character was redesigned for Metal Gear Solid 4. He was again redesigned for both the cancelled game Metal Gear Solid: Rising and its reboot Revengeance to portray a darker side of his character. Raiden is voiced by Kenyu Horiuchi in Japanese and Quinton Flynn in English.

Raiden's debut role as the protagonist of Metal Gear Solid 2 was controversial, due to his unexpected substitution for the established hero Snake. Some critics defended the character, stating that fans were merely angered by Snake's removal and that Raiden was appealing. Despite the initial mixed reception, Raiden has been praised for his role in the game, as well as his later Metal Gear Solid 4 redesign and more for his role and design in Metal Gear Rising: Revengeance.

According to series creator Hideo Kojima, the decision to make a new character to replace Solid Snake for most of Metal Gear Solid 2: Sons of Liberty stemmed from the developer's desire to develop Snake from a third-person perspective. Kojima stated that Raiden's character and his perception by the audience were important to the overall feel of the story. The idea of having a second main character was inspired by the Sherlock Holmes short stories and novels in which the narrator is Dr. Watson rather than Holmes. Kojima said that while Raiden was the playable character, Snake was still the game's true protagonist rather than Raiden. Yoshikazu Matsuhana, assistant director for the project, was uncertain about this decision; he considered Raiden a "weak-looking character" but decided to follow Kojima. The codename "Raiden" was based on that of the Mitsubishi J2M Raiden, a historical combat aircraft of the Imperial Japanese Navy Air Service. It was initially planned to be written in katakana as "ライデン", but was changed to the kanji form "雷電" because of a resemblance to Bin Laden's "Laden" in katakana, "ラーディン". His full name was going to be "Raiden Brannigan" but the idea was scrapped. The romantic relationship between Raiden and Rosemary was inspired by Kojima's experiences; their names, Jack and Rose, are a reference to Leonardo DiCaprio and Kate Winslet's lead characters in the film Titanic. In Metal Gear Solid 2, Raiden is considered to be a representation of the player through the experiences between the player and the character during the game.

Kojima conducted a survey among Japanese women about their views on certain video games. One respondent stated that she was tired of the main characters being "old men". Kojima took her complaint into consideration, and Raiden was designed by artist Yoji Shinkawa to be more appealing to the preferences of Japanese women. Some Western gamers thought Raiden had an effeminate appearance, however Shinkawa said this perception is wrong, and that Raiden's appearance is that of a handsome young man. Raiden's outfit—the Skull Suit—was difficult to design until the staff decided on a "bonelike" concept. Shinkawa wanted to make Raiden sexually appealing, emphasizing the tightness of his clothing. The design of Raiden's underwater rebreather mask was inspired by ancient mystical ninjutsu, where the ninja bites a scroll in the mouth during magic transformations. Raiden's final duel with the boss Solidus Snake was revised in the making of the game. Originally, to defeat Solidus, Raiden must cut off both his mechanical snake-like arms, then he must attack Solidus' back and sever the backbone vertebra connection, rendering Solidus no longer mobile. Following this, Raiden would finish Solidus by decapitating him similar to samurai fashion. The scene was rejected and instead, Raiden would slice Solidus' stomach, another idea taken from samurai. However, this concept was also scrapped to simply Raiden slicing Solidus' vertebral column with the boss falling from the area to give the idea he could not accept his defeat.

Konami kept Raiden's starring role in Metal Gear Solid 2 secret until the game's North American release; the company replaced Raiden with Snake in teaser trailers and other preview materials. Although Raiden appeared in several preview trailers in his scuba gear, his presence was not emphasized. The surprise to fans that Raiden was not Snake was admitted by Kojima to have been inspired by the plot twist of Terminator 2: Judgment Day where the titular character played by Arnold Schwarzenegger was not a villain in that movie. Raiden's appearance in the game was announced to the Japanese press on the day of the game's release in North America. Kojima said that Raiden was not supposed to be the focus of the storyline, even if he was the main character, and that he "didn't do a good enough job of conveying that" to the player.

Raiden's new design for Metal Gear Solid 4 was a response to the criticism that only his face remained in his cybernetic body. Shinkawa was surprised by the way he illustrated Raiden. The staff noted that Raiden's debut in the game's trailer received notably positive responses; several video-game magazines promoted the game with Raiden's screenshots. Shinkawa and Kojima initially wanted to reincarnate Gray Fox for Metal Gear Solid 4, but scrapped him for Raiden, who they "adored" and wanted to expand with another game. In designing him, Shinkawa wanted to convey both Raiden's beauty and sorrow in his cybernetic body. He was given the ability to wield swords with his own legs, giving the players the impression he was a ninja. Raiden's first fight against Vamp in the game caused motion and voice actors difficulty because of carefully planned movements performed by the two fighters. The staff was satisfied with the outcome, considering it one of the best battles in the game. Two actors were selected for the motion capture of Raiden; one did most of his appearances while another did his action sequences. Raiden's fights in Guns of the Patriots were made to assist the weaker Solid Snake and appealed to previous fans of the series who disliked the character. Because Raiden became a more active character in Guns of the Patriots, Kojima expressed a desire in him returning in a future character as playable.

When Metal Gear Rising: Revengeance was known as Metal Gear Solid: Rising, former producer Shigenobu Matsuyama hinted that Raiden's past as a child soldier would be elaborated upon and his weaknesses as a human would be explored. Matsuyama wanted Raiden to have as strong a role in the game as in Metal Gear Solid 2, leading him to become its main character. Director Mineshi Kimura wanted Raiden to be able to move the way he did in the Metal Gear Solid 4 trailers, wanting to show "the stealth of the sword, and the strength of not even losing to the gun, and the fear and power you have with this blade". Matsuyama said they would focus on Raiden's strong will and physical strength so he would be enjoyable to control. Raiden's design was changed during the game's development, leading to different promotional images of him. Following the game's reboot into a spin-off, developers stated that while Raiden "has grown up" in comparison to previous Metal Gear games, he is still conflicted with his life as a child soldier in the First Liberian Civil War, leading him to become a "hero with a dark past". Shinkawa later discussed with Platinum Games' Kenji Saito about including his quasi-human look. Raiden's loss of an eye also represents his transformation across the story while also comparing him with the previous antagonist Solidus Snake. Tamari also explained that the cybernetic functions Raiden has were based on research led by the University of Texas. In response to complaints that Rising appeared to contradict Raiden's ending in Guns of the Patriots, the Kojima Productions staff said the game would explain what happened with Raiden's life. While Steven Armstrong was the game's final antagonist, the character of Jetstream Sam was developed to be Raiden's rival, something Shinkawa and fellow designer Kenichirou Yoshimura worked together to make both of them contrast each other through their visual appearances.