SkullKnightmon is an Undead Digimon whose name and design are derived from the mythological undead knight. It is a big brother who exchanged cups of brotherhood with Axemon. As a knight which excels in cunning, its behavior is based on its policy, "Those who are knights must fight. Even more than fighting, they must win," and generally speaking, it puts importance on the outcomes in which it wins. Moreover, it will unabashedly perform any kind of unclean act to arrive at that result. It specializes in combat which capitalizes on the size of its body, and the manner in which it dives at the opponent's chest, swinging its "Spear Needle", shows off the unthinkable actions of a knight that has forgotten its pride.
SkullKnightmon is an unscrupulous Digimon who is the core persona of AxeKnightmon.
When Shoutmon X4 and MetalGreymon appear to have AxeKnightmon on the ropes, he orders Nene to use Xros Open to split him back into SkullKnightmon and Axemon, allowing him to attack each of them one-on-one. After regaining the advantage, he has Nene DigiXros him and Axemon together to SkullKnightmon Cavalier Mode, then Bigaxe Mode. Legendary Deckerdramon, Stir!
During the events of Hell's Field while Axemon counterpart was injured, placed inside the Darkness Loader to heal, SkullKnightmon goes after Yuu and bring him to Bagra Pandæmonium where he eventually recombined with Axemon back into AxeKnightmon.