How does one become a "Māra"? I am not asking for an explanation on the whole "What is a Mara?" question. What i'm asking about is the being mentioned in Buddhism who has the command over all normal beings, the one who came personally to challenge,frighten lord Buddha.

Is there an explanation to why or how a person become's a "Mara"?
Abhisankhāra-māra - The Karmic force
  
  Kleśa-māra, or Ma̋ra as the embodiment of all unskillful emotions.
  
  Mṛtyu-māra, or Māra as death, in the sense of the ceaseless round of
  birth and death.
  
  Skandha-māra, or Māra as metaphor for the entirety of conditioned
  existence.
  
  Devaputra-māra, or Māra the son of a deva (god), that is, Māra as an
  objectively existent being rather than as a metaphor.


Apart from your internal mara and metaphysical maras. The Mara as existent beings are essentially gods with Wrong Views and Wrong Intentions. The Mara that tempted Buddha in particular, was a god from one of the highest heavens Paranimmita-vasavatti, the devas with the power over other's creations. That is not only can they create anything to fulfill their desires, but other create it for them to worship them. Seeing that the Desire Realm was so enjoyable and pleasurable, why should anyone seek to leave it and so try to oppose the Buddha.

So how did such a being came about? Through their former karmic merit. Like gods who attain heaven but then squander their merits, maras went further by obstructing others in their search for virtue and truth.

Unlike the Christian devil, Maras are not rulers of Hell. But in a sense they are 'fallen' in spirit, though not in power. Eventually such a being use up their good karma and fall possibly even the the hells themselves. Of course they are not unredeemable either, if they repent and support the truth, the label 'Mara' would not apply to them.

There is a saying in Chinese Buddhism, to cultivate karmic rewards without cultivating wisdom is the Way of Mara. That is your good karma could bring you high up in the the heaven or as a ruler (or someone in position of power), but without wisdom - and therefore ethics, you could easily abuse your powers, causing suffering on others and ultimately yourself.

So as you can see, you could be your own Mara, you could be a Mara to others and discourage them from doing good deeds.