In a republic you have a sovereign, usually it's the president of that nation. I think you mean absolute sovereign. Although I think absolute monarchy is a bit of a misnomer, usually these monarchies had like a thousand bizarre ancient rituals and medieval traditions that restricted their power. The more absolutist monarchs pushed back against these, but even the most extreme pretty much never established a situation where their will was unquestionable and always respected law. At best they made pretensions of such while usually being ignored.