Kitchener was, of course, Secretary of State for War and virtual military supremo.
{i} (British Informal) boss, chief, person in charge; person with supreme skills or knowledge in a particular field
A supremo is someone who is considered to have the most authority or skill in a particular organization, situation, or area of activity. Her new role as fashion supremo is something she can really get her teeth into. supremos someone who controls a particular activity, organization, or industry, and has unlimited powers