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 Greek philosopher Theophilus.
The rim of Theophilus has a wide, terraced inner surface that shows indications of landslips. It is 14,000 feet deep with massive walls and has broken into a second formation, Cyrillus. It was created during the Eratosthenian period, from 3.2 to 1.1 billion years ago. It has an imposing central mountain, 1,400 meters high, with four summits.
The floor of the crater is relatively flat, and it has a large, triple-peaked central crater that climbs to a height of about 2 kilometers above the floor. The western peak is designated Psi (ψ), the eastern Phi (φ), and the northern peak is Alpha (α) Theophilus. The western slopes of this ridge are wider and more irregular, whereas the peaks descend more sharply to the floor on the northern and western faces.
The Apollo 16 mission collected several pieces of basalt that are believed to be ejecta from the formation of Theophilus.