Adam Neuser (c. 153012 October 1576) was a Protestant pastor of Heidelberg who held Antitrinitarian views and eventually converted to Islam.
Neuser was born in Gunzenhausen and was a popular pastor and theologian in Heidelberg in the 1560s, serving at the Peterskirche and later the Heiliggeistkirche. During the controversy over church discipline that developed in the late 1560s, Neuser became a leading member of the Antidisciplinist, and thus anti-Calvinist, faction led by Thomas Erastus. His disaffection with the ecclesiastical regime perhaps played some role in his doubts concerning orthodox Christian dogma.
He wrote letters sternly attacking the doctrine of the trinity. He wrote to the Ottoman Sultan assuring Sultan that he would receive support in Germany if his conquests push him that far. Neuser along with another Antitrinitarian, Johann Sylvan, sought to dialog with the Turks. In an unsent letter, he argued that Christianity was corrupt, that Islam was better, and therefore the Sultan should take his army and conquer Europe.
Neuser was accused of denying divinity to Jesus Christ and was consequently imprisoned. His associate, Johann Sylvan, was tortured and beheaded. Neuser confessed but managed to break out of prison. He later converted to Islam and traveled to Istanbul where he served the Ottoman Sultan. When anti-Trinitarian visitors came to Istanbul, he attempted to convert them to the Islamic faith. Neuser also continued to research Christian sources that would refute the Trinity. He read the critiques of Christianity by Muhammad bin Abdullah, a Hungarian who had converted from Christianity to Islam, and recommended them to his friends.
His letter to the Ottoman Sultan is included in "Antiquities Palatine" which is now in the Archives at Heidelberg: