Simplify the following text for a Grade 8 native English-speaking person.
Original: The first former constable to be appointed Commissioner of Police of the City of London , in March 1950 , Young entrenched there his reputation as `` the policeman 's policeman '' .
Simplified: In March 1950 Young became the first former constable to be appointed Commissioner of Police of the City of London . He built up his reputation as `` the policeman 's policeman '' .