Monarchianism is a heresy that teaches that the Oneness of God implies that the Trinity does not consist of Three Persons, but only one person, with three manifestations. This heresy was started most likely by Paul of Samosota, the Bishop of Antioch (not the Apostle). There are two different forms of Monarchianism that are most prominent, Modalism and Adoptionism.
Modern proponents of modalism include TD Jakes and other Oneness Pentecostals, Unitarians and the Contemporary Christian Music group, Phillips, Craig and Dean. There are few modern proponents of Adoptionism, although certain Word-Faith theologians have appeared to give some credibility to the heresy.