Supreme Leader Bosslar commands the antagonistic organization Gekko, dedicated to global conquest by harvesting negative energy from human emotions. He possesses a dignified presence, notably featuring a dandy mustache that complements his fearsome reputation. Despite leading an organization focused on world domination, Bosslar demonstrates unexpected consideration, such as sending a get-well bouquet and card to his incapacitated adversary Fudo Aikawa during an appendicitis recovery, revealing a capacity for kindness beneath his villainous exterior.

Within Gekko's hierarchy, Bosslar oversees high-ranking executives and commanders, including monster executives like Culverin Bear and the Princess Series warriors. He holds particularly high expectations for Reaper Princess (Desumi Magahara), recognizing her as one of the organization's most promising members. His leadership involves strategic planning, such as approving an attack on an amusement park after Culverin Bear advocated for Desumi's suggestion that the location was ideal for harvesting negative energy due to its high concentration of people.

Bosslar's background includes a connection to Blood Princess (Kira Sanzugawa), a Gekko member who harbors romantic feelings for him and works as a school nurse. While their relationship is not extensively detailed, her presence adds a layer of personal dynamics to his role. His character design draws inspiration from the "Great Leader of Shocker" in the *Kamen Rider* franchise, reinforcing his archetypal position as the highest authority within a criminal organization. No significant character evolution or personal backstory beyond his leadership of Gekko is detailed across the series or related media.