The Common Archduke (Lexias pardalis) occurs in most of South and Southeast Asia.
It is typically sighted on shaded trails and among undergrowth, often seen puddling on damp ground, or feeding on rotting fruits and other organic matter amongst forest litter.
This species exhibits sexual dimorphism where the male is black with greenish blue wing margins whilst the female (see photos) is dark brown with yellow spots on both wings.
A very similar-looking species, the Black-tipped Archduke (Lexias dirtea) which also occurs in Vietnam, can be distinguished from Lexias pardalis by the colour of the tip of its antennae.
The upperside of the tip of the antennae in Lexias pardalis is orange-brown while in Lexias dirtea the antennae are entirely black.

My Son Sanctuary, Hoi An area, Vietnam, 30 December 2023