Prothero is a richly compound character.
Firstly, he is an ex-commander of the army and was a director of Larkhill. There we can find him particularly cruel.
A Collector of Dolls
Contrasting to his cruelty, we can find a completely different man if we consider his obsession with collecting dolls. This came to be his undoing when V used this for his psychological attack.
Voice of Fate
Prothero has a powerful, and charismatic voice which is known to the population as the voice of Fate itself. This is particularly useful to the government since they can exploit it to connect to the population in a more humane way.