Hubris

On a second thought, it is actually more common for straight upright unselfish people to become corrupted when they have the power, rather than a secretly ambitious tyrant keeps a nice face for 30 years with all the struggles before reaching the top of the political hierarchy.

The former has a name in medical jargon: the Hubris syndrome.

"Most political leaders become mentally or physically incapable of sound judgment and lose their grip on reality." Lord David Owen, the former UK Labour Foreign Secretary, said. He is the one who invented the name of this condition.

(Oh, we know. They emigrate to Pluto.)

Hubris syndrome is inextricably linked with power. Indeed power is a prerequisite, and when power passes the syndrome will normally remit. The disease is more likely to manifest itself the longer the person exercises power and the greater the power they exercise.

Hubris is not the name of any person; the meaning comes from ancient Greece. A hubristic act is one in which a powerful figure, puffs up with overweening pride and self-confidence, treats others with insolence and contempt, and the one seems to derive pleasure from using his power to treat the others in this way.