Enel

Enel thinks of himself as an invincible god - quite literally. He believes that he is a divine and immortal being, with the authority to do, take or destroy whatever he pleases. As the result, he appears fearless, childish, and without a care in the world. His lifestyle is relaxed and hedonistic, and when not attending to his godly duties of smiting the natives of Skypeia, he spends his time sleeping or eating (Enel's favourite fruit is apples) in his residence, being waited on hand and foot by beautiful women. This attitude carries over to his battles, where he's hardly serious and barely annoyed - instead he's relaxed, and enjoys himself by effortlessly absorbing attacks, and humiliating his opponents. In his fight against Kamakiri, he even went to sleep in the middle of the fight, in order to prove his immortality.

Enel holds no regard for other's lives except his own, and has no moral qualms about killing thousands- instead he sees it as his godly duty, and laughs as he sends Skypeia to its doom. He is in short completely insane, which was more or less undeniable when he sets off for the moon, which he believes to be the home of God (himself). Before Luffy showed up, his fruit power and mantra ability made his God complex completely legitimate. Once Luffy began gaining the upper hand in the battle he incapacitated him, in order to remove him as a threat, and reclaim his status as "invincible" - and from this point acts somewhat cowardly, trying his best to avoid another confrontation with Luffy.

Enel appears to posses a vast knowledge of mechanics and technology, as well. He personally designed his flying ark, Maxim, and knows its inner workings inside and out; if any damage is done to the inside, he is able to repair it (assuming it's repairable). He was even able to design a stormcloud production system (known as Deathpiea), an electrical power system, and a Jet Dial failsafe for the ark, in the event that the main engines are damaged.