For Baha'is anyway...there is no such ontological being that wars with God... such as "Satan"...rather we believe it refers to the lower nature of man...
Abdul-Baha stated:
The reality underlying this question is that the evil spirit, Satan or whatever is interpreted as evil, refers to the lower nature in man. This baser nature is symbolized in various ways. In man there are two expressions, one is the expression of nature, the other the expression of the spiritual realm.
(Abdu'l-Baha, Foundations of World Unity, p. 77)
also:
"We know absence of light is darkness, but no one would assert darkness was not a fact. It exists even though it is only the absence of something else. So evil exists too, and we cannot close our eyes to it, even though it is a negative existence. We must seek to supplant it by good, and if we see an evil person is not influenceable by us, then we should shun his company for it is unhealthy."
(From a letter written on behalf of the Guardian to an individual believer, October 4, 1950: Spiritualism, Psychic Phenomena and Related Subjects p. 4, a compilation from the Universal House of Justice, February 14, 1973 to National Spiritual Assemblies)
(Compilations, Lights of Guidance, p. 512)