"Rouxls acts very egotistically... He claims to be the Duke of Puzzles, and attempts to stop the party by forcing them to solve his puzzles. However, he is an incompetent puzzle-maker; each of his puzzles consist of the bare minimum of elements -- a box and a button -- and he makes no attempt to obfuscate the solution in any way. He also vandalizes clues on puzzles he did not create, in order to make them "harder." He uses Early Modern English speech patterns, presumably to appear educated, but this amounts to little more than replacing all instances of "you" with "thou," randomly adding "-est" and "-eth" suffixes, and haphazard capitalization of phrases for emphasis. When his pride is hurt, he doubles down by intensifying his misuse of Early Modern English to the point of incomprehensibility; but when surprised or stressed, he tends to drop it altogether."  (Rouxls Kaard WIKI)

My sister describes him as sounding like a mixture of Mettaton, Papyrus and Senpai from FNF. ...I can see that! But any other similar interpretation is fine! His voice must be big and overly pompous!