Ninjak is a fictional superhero appearing in comic books published by Valiant Comics. The original incarnation of the character was created by Mark Moretti and Joe Quesada, The character was first introduced as a ninja and spy in the Valiant Comics series Bloodshot in July, 1993. His appearance in that series served to encourage interest ahead of his own self-titled series, which began in November that same year (although Ninjak vol. 1 #1 has a cover date of February, 1994). Acclaim Entertainment bought out Valiant Comics in 1996, after which Ninjak and other characters were rebooted. The Acclaim Ninjak series lasted only a year. Valiant Comics later returned and rebranded as Valiant Entertainment, and a new version of Ninjak, more in-line with the original incarnation, was introduced to readers in 2012.

The Acclaim Comics version of Ninjak is a teenager who gains the combined abilities of multiple ninja warriors by unlocking a puzzle in a video game. In both his original Valiant Comics incarnation and Valiant Entertainment reboot incarnation, Ninjak or "Ninja-K" is Colin King, a British child of wealth who becomes a master spy and ninja, then works as a special "freelance" operative for MI-6. Though not having any superhuman abilities, Ninjak's skills, intelligence, high-tech weaponry, and ninja expertise make him one of the most formidable characters in the Valiant Universe. He has also been a member of the Unity team, a group composed of powerful Valiant heroes.

The first Ninjak series was very popular. The first issue sold close to 1 million copies and was placed number one on Wizard magazine's Top Ten Hottest Comics of the month article in February 1994. Like many popular American comic series, the Ninjak comics have been translated into a number of languages, including German, Italian, Spanish, Norwegian, Filipino, and Chinese.