The Spanish interrogative pronoun 'quién' (meaning 'who') comes from the Latin accusative form 'quem' (meaning 'whom'), which itself developed from the Latin nominative form 'quis' (meaning 'who'). The evolution from Latin to Spanish involved the addition of an 'n' at the end and the development of the written accent mark to indicate stress.

Other common Spanish question words are related to 'quién', such as 'qué' (what), 'cuál' (which), and 'cuándo' (when). All of these interrogative words share a common ancestry in Latin question words beginning with 'qu-'.

While English 'who' is not directly related to Spanish 'quién' (as 'who' comes from Germanic origins), English has borrowed many words from Latin that are related to 'quién'. For example, words like 'query' (to ask a question), 'quest' (a search or pursuit), and 'inquest' (an investigation) all come from the same Latin root that gave us 'quién'. These words all share the common theme of questioning or seeking information.