Dr Mueller is co-founder of the Heraldic Institute and is currently serving as its director. He shares Anglo-German parentage with Mr Wilhelm Horwood, the Institute’s co-founder. Dr Mueller’s heraldic work includes designing new coats of arms, identifying historic ones and producing heraldic stationery, porcelain and other everyday items. One of his specialities is the identification of crests on heraldic china and silver, which he is frequently asked to do by the leading antique sellers of the United Kingdom. He is supplier of all things heraldic to royalty, aristocracy, clergy and universities.
After finishing his PhD at the University of Cambridge under Regius Professor Sir Richard J. Evans, Dr Mueller and his research featured in television documentaries in the UK and Germany. He is a regular contributor to Country Life magazine and his book The Kaiser, Hitler and the Jewish Department Store was published in May 2022 with Bloomsbury.
He a Fellow of the Royal Historical Society.
Has has worked as a professional fundraiser for the University of Cambridge and has volunteered for several charitable organisations, including the Order of St John, the LM Kendon Settlement, the League of Mercy and organisations of the Church of England.