Yoshiyuki Sadamoto (貞本 義行; Sadamoto Yoshiyuki) (born 1962, in Yamaguchi Prefecture, Japan) is one of the founding members of the Gainax anime studio.

He is also the character designer for the anime series Neon Genesis Evangelion, as well as the author of the Neon Genesis Evangelion manga series, which is also Sadamoto's first full manga work.

In addition to his work on Neon Genesis Evangelion, Sadamoto did character designs for Nadia, FLCL, .hack//SIGN and Gunbuster 2 . In 2003, Viz published a collection of his works, entitled Der Mond.