Gendo Ikari (Japanese: 碇 ゲンドウ, Hepburn: Ikari Gendō) is a fictional character from the Neon Genesis Evangelion franchise, created by Gainax. In the original anime series with the same name, Gendo is the supreme commander of the special agency Nerv, which is dedicated to the study and annihilation of Angels, a series of mysterious enemies of humans. Gendo is grief-stricken by the sudden death of his wife Yui, and abandons his son Shinji Ikari to devote himself to a plan named Human Instrumentality Project. Years later, Gendo asks Shinji to pilot a giant mecha named Evangelion; his pragmatic, cold, and calculating attitude leads him to use any means to achieve his personal goals. He also appears in the franchise's animated feature films and related media, video games, the original net animation Petit Eva: Evangelion@School, the Rebuild of Evangelion films, and the manga adaptation by Yoshiyuki Sadamoto.

The character, who was originally conceived as a modern version of Victor Frankenstein, is inspired by the personal experiences of the series' production staff, reflecting the absent, emotionally detached Japanese father figure. Neon Genesis Evangelion director Hideaki Anno's abusive father particularly influenced Gendo; the director also took inspiration from psychoanalytic concepts, especially the Freudian Oedipus complex, for his development.

Critics have negatively received Gendo, describing him as one of the meanest characters and one of the nastiest parents in Japanese animation history. Reviewers criticized his unscrupulous, abusive ways, while others were more appreciative of his role in spin-offs and the manga adaptation of the series. Reviewers appreciated Gendo's role in the theatrical saga Rebuild of Evangelion, and particularly in the film Evangelion: 3.0+1.0 Thrice Upon a Time (2021), and commented positively on his character development. Gendo's typical pose with hands clasped at mouth level has become popular, and has been homaged in other anime and manga. Merchandise featuring the character has also been released.

Hideaki Anno, the Neon Genesis Evangelion anime series director and main screenwriter, took Gendo's name from a character in a failed Gainax studio project, an anime that was planned before Evangelion but was never produced. For his bachelor name, he chose the word rokubungi (六文儀; lit. "sextant"); for his married name, he chose Ikari (碇; lit. "anchor"), to connect to the names of other characters in Neon Genesis Evangelion, inspired by nautical jargon and ships of the Imperial Japanese Navy. The character was designed by Yoshiyuki Sadamoto, mangaka of the comic version of the series. Sadamoto was influenced by the British television series UFO and modeled his relationship with Kozo Fuyutsuki on that between Commander Ed Straker and Colonel Alec Freeman from the classic series.

The show's production staff chose interpersonal communication, specifically intergenerational communication, as a central theme of the series to reflect on the lack of communication and relational difficulties of the modern world. For the psychology of the character, the protagonist's father who is unable to emotionally communicate with his son, the director took inspiration from his personality, just like all the other characters in the series. The special agency Nerv, in particular, was conceived as a metaphor for Gainax studio; Anno also described Gendo as a representation of his shadow, the dark, unconscious side of an individual's psyche. The director stated he did not conceive Gendo as a concrete father with a blood tie to his son but as a representation of society, adding; "I don't think I projected that much [into him]".

Gendo was influenced by the personal experiences of staff members, including that of Hideaki Anno, whose father injured his left leg with a power saw in a youthful accident, forcing him to wear a prosthesis. According to Anno himself, his father became emotionally unstable as a result of the accident and he grew up in a tense family environment, marked by physical and emotional punishment from his father. According to Kazuya Tsurumaki, assistant director of the series:

A lot of families in Japan a generation ago—and perhaps even now—had fathers that were workaholics and never home. They were out of their children's lives. My own father was like that, and I hardly ever got to associate with him until quite recently. I'm the same sort of person as Hideaki Anno. That probably influences the type of anime I create.

In the early design stages of Neon Genesis Evangelion, Gainax decided to portray Gendo as a "mysterious person in behavior and words", a staunch defender of the Instrumentality Project, expressive, tumultuous, akin to a twenty-first-century Dr. Victor Frankenstein. Over time, he would become obsessed with research, justifying any means to achieve his goal to the point of transforming his own body and becoming a digitized human being. His goal, however, would be benevolent, in the belief he could realize a utopian dream capable of bringing true equality among people. In the first episode of the series, Gendo would have called Shinji to fight against an Angel named Raziel, and in the fourth episode, titled "Fourteen years, the first day" (14歳、 始まりの日, 14-sai, hajimari no hi), he would have ignored his son on his birthday, but these ideas were discarded during the show's production.