Mait' Carrefour (also known as Kalfu) is the voodoo loa of crossroads, the moon, and magic. When you hear a blues singer going on about making deals at crossroads, he's the guy they're talking about, not that other guy who’s always getting the credit ‘round here.
His Rada aspect, Papa Legba is widely considered to be the 'good manifestation', who opens the gates to the spirit world, allows the spirits of good luck crossover, and is the aspect connected to light, day, the sun, and wisdom.
Kalfu is not.
Kalfu is the Petro aspect and the loa of darkness and fire. His crossroads duties include letting pass the malevolent spirits. Fear, hatred, anger- those are his. You had a nightmare recently? That's his too. But just as he lets them in, he’s also the one with the power to call them back and send them home again. He denies that he is a demon, and would like to remind everyone that, despite syncretization and what those of a certain religious bent like to say, he is not Satan, thank you.
He is also the loa of magicians, sorcerers, warlocks, enchanters, the Bokor- basically anyone who’s ever touched magic before should throw up a little thank you every once in a while. (He prefers rum with gunpowder mixed in, though he’ll take some cigs if you’ve got any).
And because very few things in this world are straight up good an evil, it must be said that just as Papa Legba and the other Rada can be used to malevolent ends, Kalfu and the other Petro can be called on for benevolent ones. While there is no such thing as real good and evil amongst the loa ('hot' and 'cold' would be better differentiators), Mait' Carrefour is one of those who comes closest to breaking the tradition and going into complete monster territory.
It helps if you think of him and the other Petro as the token evil teammates of the spirit world.