The Japanese anime television series Neon Genesis Evangelion has an extensive cast of characters that were created by Gainax. The show's protagonist is Shinji Ikari, a teenage boy whose father Gendo recruits to the shadowy organization Nerv to pilot a giant, bio-machine mecha called an Evangelion and fight against beings called Angels.

The character designs were drawn by the artist, Yoshiyuki Sadamoto, who designed each character to be easily identifiable from their silhouette. The personalities were based on that of Hideaki Anno, the show's director and main scriptwriter. Many of the heroes in the second half of the series suffer trauma or physical violence that exacerbates their anxieties and fears, and the episodes give ample space to their inner monologues, in which they question the meaning of their actions and lives. This narrative choice culminates in the two final episodes, whose narrative pivots on Shinji's streams of consciousness; the finale, however, does not clearly conclude the plot.

In Japan, the characters received favorable audience reception, becoming the subjects of merchandise and winning popularity polls. Critics had mixed feelings about their psychological exploration; some reviewers appreciated their complexity and depth and praised Anno's script, but others found the characters to be stereotypical or problematic, and disliked the insistence on their weaknesses and characterization. The show's last two episodes proved to be controversial, since the plot is eclipsed by moments of introspection. Neon Genesis Evangelion characters, especially Rei Ayanami, also inspired later anime series, creating or helping to spread new stereotypes in Japanese animated productions.

The studio Gainax studio chose interpersonal communication as the main theme of Neon Genesis Evangelion, insisting on portraying inter-generational relationships, such as those between parents and children. The studio wanted to create a series that reflects on the lack of communication in contemporaneous Japanese society, which was considered to be in ruins. The director of the series, Hideaki Anno, an otaku since his youth, experienced depression after the conclusion of his previous anime series, Nadia: The Secret of Blue Water, and poured his emotions into Neon Genesis Evangelion, making it a reflection of his feelings:

I tried to include everything of myself in Neon Genesis Evangelion – myself, a broken man who could do nothing for four years. A man who ran away for four years, one who was simply not dead. Then one thought. "You can't run away," came to me, and I restarted this production. It is a production where my only thought was to burn my feelings into film. I know my behavior was thoughtless, troublesome, and arrogant. But I tried. I don't know what the result will be. That is because within me, the story is not yet finished. I don't know what will happen to Shinji, Misato or Rei. I don't know where life will take them. Because I don't know where life is taking the staff of the production.

— Hideaki Anno

For each character, Anno took cues from a part of his personality, stating that: "All the characters of Evangelion are me". Shinji, for example, was conceived as a mirror of his self: "both the conscious and unconscious part". According to him, moreover, Kaworu Nagisa and Gendo Ikari represent his shadow, the dark, unconscious side of an individual's psyche. Kazuya Tsurumaki, assistant director of the series, stated that the autobiographical intent can also be detected in the female protagonists and secondary characters, such as Misato Katsuragi, Rei Ayanami, and Ryoji Kaji, saying, "Every character is ultimately the same. On the surface, different 'seasonings' have been used, but inside [the characters] are very similar". Anno also said Shinji and the other main characters are not to be considered only a mirror of his personal experience but a reflection of the other members of the series' creative staff as well. According to him, "It's strange that Evangelion has become such a hit – all the characters are so sick!"

In 1993, about two years before the series aired, the production studio established a temporary lead on the creation of the characters in a presentation document titled New Century Evangelion (tentative name) Proposal (新世紀エヴァンゲリオン (仮) 企画書, Shinseiki Evangelion (kari) kikakusho; Proposal). Much of them were already outlined, despite differences in script. Anno did not follow a well-defined plan for the development of the protagonists; he improvised as the episodes passed and following his instincts, as in a "live performance". The original project also included a girl character named Yui Ichijō who was similar in appearance to Rei but had dark hair; this character never appeared in the final version of the show.