Jarett

Jarett is the cruel king of the Pantophage. He looks like a red giant overweight devilish alien.

Alien Force
Jarett only appeared later in the episode Con of Rath, after he ate the Tiffin as a peace-treaty until Rath jumped down Jarett's throat and took him out, breaking Jarett's teeth in the process. Jarett threatened war against the Lewodans, but Rath threatened him about knitting his intestines into a sweater which scared him into making a peace resolution.

Kevin is apparently unaware of Jarett's planet's customs, as he faints from the shock when Jarett eats Tiffin.

Comics
In the Ben 10: Ultimate Alien toy line, there is a 2-pack containing Rath and Sixsix. The 2-pack comes with a comic published by DC Comics. The title of the comic is "Target Rath," featuring Jarett as one of the main villains along with Sixsix and Kraab.

Ben 10: Alien Force

 * Con of Rath (first appearance)

Ben 10: Omniverse

 * TBA (first re-appearance)

Comics

 * Target Rath

Trivia

 * Jarett vaguely resembles Kil'jaeden of the Warcraft series. He also bears resemblance to Trigon from Teen Titans.
 * When he ate the Tiffin, it made Jarett similar to Kronos, from Greek mythology.