Johann Arndt was an influential German Lutheran pastor and theologian. He is best known for his devotional book, Vom wahren Christentum (True Christianity), which became one of the most widely read books in Protestantism. His work emphasized mysticism and practical piety, influencing later movements such as Pietism and the work of figures like Philipp Spener and John Wesley. Despite facing controversy during his lifetime, his writings left a lasting legacy on Christian spirituality and devotion.