Charles V comes to mind, though he retired more of frustration and weakness in old age than out of principle. But his release of powers was highly unusual and had some complicated consequences.
A more precise example is Nelson Mandela. He might have run for another presidential term and become a leader overstaying his power as so many African resistance leaders have become eventually. But he chose not to, and this was a great boon to the stability of South Africa.
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Sulla (supposedly). Sulla, one of the Optimates in the Senate, beat Marius in a Civil War and established himself as a dictator in Rome in 82 BCE,. Much of what Sulla did as dictator is and was regarded as infamous, such as his widespread use of proscription to bump off his enemies and claim their property.
After doing his business, Sulla reportedly gave up on power one day in 79 BCE and withdrew into private life as if nothing had happened. Juvenal refers to his having to have composed 'advice to Sulla' poetry in his schooling in Satire 1.16-17:
"The despot should now retire into private life, Take a good long sleep".
'Exercises' of this kind (suasoriae in Latin) were common in Roman education; the idea was to compose declamations 'to be put in the mouth of' or directed at some great man of history. Other examples by the Elder Seneca survive.
Granted, Sulla's supposed peaceful resignation was after a reign of terror and bloodshed, but his 'returning to the simple life' is relevant to this question in my opinion.
Sources and further reading:
Juvenal's Satires (Peter Green translation plus footnotes).
Pope Benedict XVI