Four Sky Kings
The Four Sky Kings, also known as Shitenno (???), were Lordgenome's last project as the Green Testament. After creating and assembling Beastmen from that world, he needed to find something to lead them, and the Four Sky Kings were born.
History
The Four Sky Kings were the four Generals of the Spiral King back in his home world. They were eventually defeated by Gurren-Lagann and the Dai-Gurren Dan, and did not survive the experience. However, these four generals each had a role in the Spiral King's army, and they were useful.
Upon resurrection by Wilhelm, the Green Testament, formerly the Spiral King, he assembled the already present Beastmen, and started making more. With the high technology available at Unsichtbar, the Green Testament was able to make powerful replicas and DNA combinations, resulting in the new Shitenno. However, they were incomplete at the time of his betrayal to Asgard. To counter this, Wilhelm has created his own versions of the Anima Relics, called a Diabola Relic designed to channel his own power into them in lieu of the Spiral Energy required to actually use a Gunmen at full power.
The Four Sky Kings
The current roster of the Four Sky Kings is a simple one, each commanding a military force, one of Earth, one of Water, one of Air, and the last one being versatile in all three. They are expected to act as a group and the will of Wilhelm makes sure they have no choice in the matter.
Choleric
Choleric is the last of the Four Sky Kings to be 'born', and is a mixture between a Bat and a Rat. He is highly adaptable and a natural leader. That's why he leads the 'Marines' squadron of the Beastmen Army, assisting the other three and usually taking charge on the battlefield if decisive action is needed. He is a bit of a brat and hard to get along with, however.
Melancholic
Melancholic is the first of the Four Sky Kings to be birthed, and the most introverted and thoughtful. Arguably the smartest and the 'strategist' of the bunch, she is a capable leader but usually lets her men deal with with situations as it comes. Her orders are always followed, however. She is in charge of the Beastmen Navy. She was based on a narwhal and a stingray.
Phlegmatic
Phlegmatic is the most relaxed and patient of the Four Sky Kings. He has all the time in the world and would rather relax than fight, but when his ire is raised he is quite the deadly fighter, patiently stalking and defeating his opponents. He does not get along with Melancholic at ALL, and would rather never have to deal with her, but Wilhelm's desirs supercede his. He was made from the mixture of a cat, a dog and a wolverine, and such leads the Ground Forces of the Beastmen Army.
Sanguine
Sanguine is the third 'born' of the Four Sky Kings, and she is the most 'out there'. Thrill-seeker, hedonistic and sadistic to the extreme, Sanguine rules the Air Force of the Beastmen Army. She is flighty and easily distracted, but absolutely relentless if she declares you her enemy. She is a viciously dangerous opponent in a fight, harassing and focussing all her attentions on a single target. She was made from the DNA of a flying squirrel and a sparrow, as well as a touch of beetle.