The official announcement by the Antiochian Archdiocese my be read at http://www.antiochian.org/content/fr-peter-gillquist-retire-head-department-missions-and-evangelism-fr-michael-keiser
Father Michael is probably most known for his book A Beginner's Guide to Prayer: The Orthodox Way to Draw Closer to God
, Conciliar Press,, 2003. I knew him as the priest at St Anthony's in Tulsa Oklahoma,where he caused a stir when a professor and many students at Oral Roberts University Seminary were converted to Holy Orthodoxy. Indeed, five of those converts are now prominent priests in the Archdiocese, including the current rector at St Anthony, Archpriest George Eber, and the rector of St Elias in Austin (my church when I was living there), Archpriest David Barr.
By way of a short bio, here is the "About the author" blurb in his new book, A Beginner's Guide to Spirituality, The Orthodox Path to a Deeper Relationship with God, Conciliar Press, 2007:
"The Very Rev. Michael Keiser is a convert to the Orthodox faith who was raised in the Western Christian tradition. He has studied in both the Western and Eastern traditions of Christianity, and has been actively involved in evangelism and outreach on behalf of the Orthodox Christian Church. An Orthodox priest for thirty years, he has served his entire ministry as part of the ancient, biblical Church of Antioch, both in the United States and Europe, and currently works in the Department of Missions and Evangelism of the Antiochian Archdiocese. During his career he has worked with 28 different congregations in the areas of renewal and growth, established new congregations, and guided many who have found a true home in Orthodox Christianity. Fr. Keiser has written five books dealing with worship, spirituality, and an Orthodox comprehension of suffering. He currently lives in Florida with his wife of 39 years, Angelina."