Complex sentence: Stratford served for a time as deputy to his brother, John de Stratford, in 1331 became Chancellor of the Exchequer and in 1337 Lord Chancellor Fryde, et al.
Split into simpler sentences: Stratford served for a time as deputy to his brother John. In 1331 became Chancellor of the Exchequer and in 1337 Lord Chancellor Fryde, et al.