Leaders: In human society: Those with power or influence, whose commands are followed or whose ideas adopted.
It is a curious and important fact about the human animal that most men follow leaders, and are conformists and followers. In part this seems due to humans being social animals; in part to the fact that relatively few are intelligent, independent, or strong; and in part to the fact that every human being spends the first 15 or 25 years of his life as a weak dependent of stronger and larger adults.
Also, there are three other things about leaders that should be noted:
First, there is Lord Acton's observation, as he in fact made it: "Power tends to corrupt, and absolute power corrupts absolutely. Great men are almost always bad men, even when they exercise influence and not authority, still more when you superadd the tendency or the certainty of corruption by authority."
Second, and conversely, it is especially the corrupt that seek power and that acquire power: They desire it to be able to abuse it, and they have better chances than the non-corrupt to acquire it because they have fewer or no inhibitions to lie, to pretend or to use or - more often - to incite to violence to get their own way.
Third, since political parties are voluntary associations of people that seek social power for their leaders, so that the leaders and their followers can realize their political ends and/or acquire personal advantages (after Max Weber), the chances are that both the leaders and the members of political parties are a particular type of person, that are more like psychopaths - characterized in terms of "coldheartedness, egocentricity, superficial charm, manipulativeness, irresponsibility, impulsivity, criminality, antisocial behavior, a lack of remorse, and a parasitic lifestyle " (Wikipedia) - than the members of non-political voluntary associations.