Legba, a god of West Africa and Voodooism, is the child of the Sky Pantheon. He is allied with destiny, but has no particular domain. Legba is very intelligent and cunning, despite the fact that he is a trickster. Although Legba appears as a weak poorly dressed old man, he is really very strong. He understands all languages of humans and of the gods. In Voodoo ceremonies, Legba is always the first to be invoked. No Loa, a spirit of the dead, is allowed to enter into the worshippers unless he has Legba’s permission. This is because he holds the key to the gate separating the humans’ world and the world of the gods.
Papa Limba, or Labas, is who we refer to as Papa Legba today; and St. Peter is the Catholic saint syncretized with him. Papa Legba is the gatekeeper to the spirit world and is represented by keys, among other things, while St. Peter holds the keys to the gates of heaven. Beyond this similarity, however, the two have little in common.
In New Orleans Voudou, syncretism manifests as Catholic icons representing African deities. The introduction of Catholic saints is a direct result of the implementation of the Louisiana Black Code, which made the practice of any religion other than Catholicism illegal. Substituting images of Catholic saints that shared similar characteristics as the Voudou spirits allowed slaves to continue with their religions in a veiled manner. Over time, the saints became incorporated into New Orleans Voudou as separate entities unto themselves, not substitutions. In Louisiana, it was easy to blend Voudou and Catholicism because of the many similarities between the two traditions. Both believe in a supreme being, include symbolic or actual rituals of sacrifice, and both use altars as focal points of devotion.
Source: The Magic of Marie Laveau