Reptyl showed him mercy by not killing him, realizing that he was under mind control. In fact, when Reptyl became worried of his area of space being controlled he left all his men on a planet with a weapons cache and put Clumsy in command.
Clumsy always craved power of his own and thought very highly of himself, although he was really aptly named. He was manipulated again by the Contemplator to betray Reptyl. He gave up the location of the weapons cache to the Kree. He agreed to betray Reptyl himself stabbing him in the back during a battle which the Kree won.
He was a hero to the pink skinned Kree. Recognition and stardom is all that Clumsy had dreamed of and now he had it. This was a further manipulation by the Contemplator who wished the tension to build so he could take over as Supremor. Contemplator promised him great power in the empire, but Clumsy betrayed him. He sought out a wizard, and the pink Kree brought him to the Cotati. The Cotati believed it would be better to have Clumsy as emperor than the Contemplator. They used their power to foil the Contemplator’s plans and drive him mad. Clumsy was placed as Emperor of the Kree.
But this was short lived and he was assassinated by a robot that looked like the Silver Surfer. This robot was all part of a plot for Ael-Dan and Dar-Benn to take control of power.