Theorein

Theorein was a late-20th-century Swiss watch brand closely associated with complication specialist Kelek. Watches signed Theorein, Kelek Theorein or similar appeared especially in the 1980s–1990s, including jump-hour, triple-calendar, perpetual-calendar and chronograph pieces—sometimes in precious metals, as seen at auction.

Kelek’s own roots go back further (Gorgerat family; Kelek SA brand from 1960) and the firm was acquired by Breitling in 1997. Theorein itself left limited standalone corporate documentation; surviving references are mainly catalogues, auction lots and collector forums, so a precise independent founding year is not confidently verified.