The designation Skull Leader signified the commander of the Skull Squadron, which was a squadron composed of Mandalorian starfighters. Around 19 BBY, specifically during the Third Battle of Mygeeto, Fenn Rau held the position of Skull Leader. In this role, he commanded his Fang fighters against formations of B1 battle droids, providing protection for Jedi General Depa Billaba and her allied forces within the Southern Mesas region.
The responsibility of Skull Leader was to command Skull Squadron, a squadron of Mandalorian starfighters of the Fang-class. When Fenn Rau, a Mandalorian Protector, was Skull Leader, he was distinguished by wearing protector armor adorned with blue markings.
During the Clone Wars, around 19 BBY, the third battle of the planet Mygeeto in the Outer Rim saw Fenn Rau serving as Skull Leader. This conflict was part of the larger war between the Galactic Republic and the Confederacy of Independent Systems. In this role, he led his squadron against formations of battle droids.
In a span of just two minutes, Rau and his squadron successfully eliminated a contingent of B1 battle droids situated in the Southern Mesas, thereby rescuing Jedi General Depa Billaba, Jedi Commander Caleb Dume, Clone Captain "Styles," and clone trooper Stance. Rau's intention was for their actions to demonstrate that some Mandalorians still possessed honor and duty. After their attack, the squadron departed, preventing Dume from expressing his gratitude to Skull Leader. On another occasion, Skull Leader Rau piloted his Fang fighter through a volcanic landscape. Later in life, Rau considered his actions as the product of youthful idealism. However, Dume, who had since adopted the name "Kanan Jarrus," finally encountered him in 3 BBY on the third moon of Concord Dawn, a planet in the Outer Rim, and recalled Rau's actions during the Clone Wars.