I need a word to call someone who inserts themselves into a power void without permission. Or someone takes a title before proving that they've earned it. The chosen one is dead, a guy takes his weapon and won't give it to the speaker, the speaker thinks the guy might have arranged the chosen one's death. Upstart doesn't have the right punch and its synonyms are about wealth. Despot is completely the wrong direction. I tried inserting the czech word for "climber" but I think I'd rather have the english word if there is one.