The word 'who' has a long lineage tracing back to the Proto-Indo-European interrogative root kʷo-, meaning 'who? what?'. This root gave rise to similar question words across many Indo-European languages. In Proto-Germanic, it evolved into hwaz, which became 'hwā' in Old English. Over centuries, the spelling simplified from 'hwa' to 'who', and its function solidified as the primary pronoun for inquiring about or referring to a person or people, distinct from 'what' for things. Its journey reflects a common pattern where a fundamental, ancient interrogative element remains stable in core vocabulary.

The word 'who' is an Old English interrogative and relative pronoun. It is a simplex word derived from the Proto-Germanic hwaz, which in turn comes from the Proto-Indo-European interrogative stem kʷo-.