What does Roy mean?
From Old French 'roy/roi', meaning 'king'. Note a second, separate origin: the Scottish Gaelic nickname 'ruadh' ('red', of hair/complexion) — so Roy can mean 'king' (French) or 'red' (Gaelic) depending on the bearer.
What does Leroy mean?
From the Old French 'le roi', meaning 'the king', originally a Norman nickname or occupational byname. A literal 'the king' name.