Distinctive Characters: Dorsal fin with 13-14 spines and 18-21 rays. Anal fin with 3 spines and 18-21 rays. Pectoral fin rays 19-20. Body depth 1.6-1.8 in standard length. Soft dorsal fin develops a point with growth. Posterior margin of preopercle finely serrate. Caudal fin rounded.
Colour: Sides with alternate blue and yellow stripes. Dorsal fin mainly yellow, caudal yellow, and anal blue and black. Black face mask with blue edge. Juveniles deep blue with curved circular white bands.
Habitat and Biology: Solitary. Usually seen on exposed outer reef areas near edges and caves in rich coral areas up to 25 m. Feeds primarily on sponges.
Remarks: Adults of Pomacanthus imperator form territories which they defend vigorously against other members of the same species. Even individuals of the two sexes come together only to breed.