Chopsuey, also known as Experiment 621 ("six-two-one"), is one of Jumba Jookiba's genetic experiments in the Lilo & Stitch franchise. A green furred, koala-like alien creature with a yellow Mohawk, he is an antagonist of the PlayStation 2 video game prequel, Disney's Stitch: Experiment 626.

He was designed for the same purposes as Experiment 626 and has much of the same powers as his younger "cousin", but is not as capable as 626, which made 621 very jealous of his successor. Criticized and neglected by Jumba for being ineffective at collecting DNA, 621 secretly collected DNA for himself and used it to mutate into a larger, stronger creature. However, 626 managed to defeat him in battle.

621 did not appear in any of the franchise's sequel material, although Leroy & Stitch gave him the name "Chopsuey" in its credits.

Pointless side note: he is not the inspiration for the name of e621. (Another pointless side note: besides that, experiment numbers are sometimes prefixed with "X-" as a shorthand for the word "experiment", not with an "e".)