Theophilus is a prominent lunar impact crater that lies between Sinus Asperitatis in the north and Mare Nectaris to the southeast. It partially intrudes into the comparably sized crater Cyrillus to the southwest. To the east is the smaller crater Mädler and further to the south-southeast is Beaumont. It was named after the 4th-century Coptic Pope Theophilus of Alexandria. Theophilus, Cyrillus and Catharina form a prominent group of large craters visible on the terminator 5 days after the new moon.