I get the distinct impression that many dictators bear the military rank of colonel - for example, Muammar Gadaffi held the rank of colonel while ruling Libya (and is indeed more commonly known in the West as 'Colonel Gadaffi' than by his actual first name), and Georgios Papadopoulos was a colonel while heading the Greek military junta.
My question is: why colonels? Colonel is not the highest army rank - above them are various grades of generals, and (depending on the country and the era) quite possibly higher ranks still, usually including the word 'Marshall' somewhere.
Even if a dictator sees no need to appoint themselves to ludicrous new ranks like 'Most Supreme Marshal' or 'Eternal General of the People' or something like that, I don't understand why Gadaffi, Papadopoulos and others did not at least take on the highest available grade of general - when not doing so presumably resulted in them, as head of state, giving orders to military officers of higher rank than themselves.
EDIT: to clarify, I am aware that many dictators with a formal military rank are actually generals or marshals of some sort, and that the colonels I described are in the minority. My question wasn't why this practice is universal (because it's not), but why it exists at all.