The emperor angelfish is one of the best-known and most widespread angelfishes. It reaches a length of 40 cm. The distinguishing color of the adult are a blue body crossed with diagonal yellow lines, a yellow tail, a light blue mouth and a blue-edged black band over the eyes. Juveniles are strikingly different having a pattern of concentric blue and white lines on a black body.

Emperor angelfish are relatively common and, as adults, inquisitive animals which may come quite close to divers. They are found on both coral and rocky reefs from shallow water down to depths of about 50 m. They live in pairs and swim about the reef with graceful unhurried movements. Although generally seen alone, the partner is usually nearby.

Emperor angelfish feed predominantly on encrusted sponges with algae but other invertebrates are also eaten.