One who brownnoses (flatters or humors somebody in an obsequious manner for personal gain); one who sucks up; a bootlicker, ass-kisser, sycophant.
A person who rules or governs; someone or something that exercises dominion or controlling power over others.
A (usually rigid), flat, rectangular measuring or drawing device with graduations in units of measurement; a straightedge with markings.
To beat with a ruler (as a traditional school punishment).