Simplify the following text for a Grade 11 native English-speaking person.
Original: He was Commissioner of Police of the City of London from 1950 to 1971 and was also the first head of the Royal Ulster Constabulary to be called the Chief Constable , instead of Inspector-General .
Simplified: He was Commissioner of Police of the City of London from 1950 to 1971 and was also the first head of the Royal Ulster Constabulary to be styled Chief Constable .