In New World Vodou, the spirits (lwa or loa) with whom believers interact are divided into three main families, Rada, Petro, and Ghede. Lwa can be viewed as forces of nature, but they also have personalities and personal mythologies. They are extensions of the will of Bondye, the ultimate priciple of the universe.
Rada lwa have their roots in Africa. These were spirits or deities honored by enslaved Africans who were brought to the New World, and became the major spirits within the new religion synthesized there. Rada lwa are generally benevolent and creative, and are associated with the color white.
Rada lwa are often considered to also have Petro aspects, which are harsher and more aggressive than their Rada counterparts. Some sources describe these different personalities as aspects, while others depict them as separate beings.
Petro (or Petwo) lwa originate in the New World, specifically in what is now Haiti. As such, they do not appear in African Vodou practices. They are associated with the color red.
Petro lwa tend to be more aggressive and are more often associated with darker subjects and practices. To divide up the Rada and Petro lwa in terms of good and evil, however, would be highly misrepresentating, and rituals dedicated toward assistance or harm of another can involve lwas of either family.
Ghede lwa are associated with the dead and also with carnality. They transport dead souls, behave irreverently, make obscene jokes and perform dances that mimic sexual intercourse. They celebrate life in the midst of death. Their color is black.