Xylotrupes gideon are among the world’s largest beetles; the males can be 6 cm long.
The males may be a shiny reddish brown, dark brown or completely black. They have two bifid (forked) horns. The first curves upward and projects from the insect’s head. The second, larger, horn is an extension of the pronotum (the front part of the thorax).
Young males are lighter in colour and have smaller horns.
The females have no horns and are generally a dull black.