In New World Vodou, the spirits (or lwa) 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 LoaRada lwa have their roots in Africa. These were spirits or deities honored by slaves 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 LwaPetro (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.