The series is currently in its second season as of May 4, 2018
The series follows the titular character, K.O., and his efforts to become the world's greatest hero, while working at Gar's Bodega (run by the no-nonsense Mr. Gar), a hero supply shop in the Lakewood Plaza strip mall. Alongside him are his best friends and co-workers Radicles, an apathetic, selfish alien, and Enid, a levelheaded big sister-like employee, as well as other heroes who work and frequent the area.
- Radicles (Rad)
- Mr. Gar
- A Real Magic Skeleton
- Mr. Logic:Lord Boxman first robot.
- Ms. Mummy
- Red Action
- Bell Beefer
- Mega Football Baby
- Nick Army
- Joff the Shaolin Monk
- Punching Judy
- Ted the Viking and Foxy
- Shy Ninja
- Rippy Roo
- Laser Blast
- Joe Cuppa
- Crinkly Wrinkly
- Dynamite Watkins
- Lord Boxman:the main antagonist of Series.
- Darrell:was the new owner of Boxmore until Venemous by back
- Boxman Jr.
- Professor Venemous
- Shadow Figure
- Miss Quantum/Bad Apple
- Chameleton Sr.
- Chameleton Jr.
On September 29, 2017, a crossover between OK K.O.! Let's Be Heroes and Ian JQ's original webcomic RPG World titled "A Hero's Fate" aired. When a long-lost hero stumbles into Gar's, KO agrees to help him complete his years long quest.
Captain Planet and the Planeteers
On October 9, 2017, a crossover between OK K.O.! Let's Be Heroes and Captain Planet and the Planeteers titled "The Power is Yours!" aired. When Lord Boxman is trashing the Plaza with pollutants, K.O, Rad, and Enid recruit Captain Planet to help.
On August 23, 2018, the series finale of Mighty Magiswords, titled "Let's Team Up Because We Aren't Bad Friends" was released on the CN app. It featured a minor appearance of OK K.O.! Let's Be Heroes character, Radicles. Prohyas would later make an appearance in "Crossover Nexus".
On October 1, 2018, a Halloween special of OK K.O.! Let's Be Heroes was released on the CN app, it features characters from Ghoul School as Enid's friends. The special is titled "Monster Party".
On October 8, 2018, a special crossover episode featuring K.O. from OK K.O.! Let's Be Heroes, Garnet from Steven Universe, Raven from Teen Titans Go! and Ben from the 2016 Ben 10 reboot aired. The plot involved KO finding himself trapped inside an mysterious place, where he encounters other Cartoon Network Heroes and they band together to escape.
The special featured cameos of various other characters from many other Cartoon Network series, such as: I Am Weasel, Hi Hi Puffy AmiYumi, Chowder, Ed, Edd n Eddy, The Moxy Show, Adventure Time, Regular Show, The Powerpuff Girls, The Amazing World of Gumball, Uncle Grandpa, Secret Mountain Fort Awesome, Johnny Bravo, Whatever Happened to Robot Jones?, Codename: Kids Next Door, Sym-Bionic Titan, Sunday Pants and many more.
The series got a 4/5 on Common Sense Media and a 8.2/10 on IMDb.