“Plato said that virtue has no master [Republic 617e]. If a person does not honor this principle and rejoice in it, but is purchasable for money, he creates many masters for himself.”

Dialogue on the Soul and the Resurrection, Patrologia Graeca 46.101-105

Source: Words of a Sage : Selected thoughts of African Spir (1937), p. 39, with a quote from Galatians, IV, 6-8.

As quoted in Chess and Computers (1976) by David N. L. Levy, p. 40

Variant: He who conquers others is strong; He who conquers himself is mighty.

Records of the Grand Historian
Source: Translated by Burton Watson. Shiji 129: The Biographies of the Money-makers.

Sixth Thesis
Variant translations:
Out of the crooked timber of humanity, no straight thing was ever made.
Out of timber so crooked as that from which man is made nothing entirely straight can be built.
From such crooked wood as that which man is made of, nothing straight can be fashioned.
Idea for a Universal History from a Cosmopolitan Point of View (1784)
Context: The master is himself an animal, and needs a master. Let him begin it as he will, it is not to be seen how he can procure a magistracy which can maintain public justice and which is itself just, whether it be a single person or a group of several elected persons. For each of them will always abuse his freedom if he has none above him to exercise force in accord with the laws. The highest master should be just in himself, and yet a man. This task is therefore the hardest of all; indeed, its complete solution is impossible, for from such crooked wood as man is made of, nothing perfectly straight can be built. That it is the last problem to be solved follows also from this: it requires that there be a correct conception of a possible constitution, great experience gained in many paths of life, and — far beyond these — a good will ready to accept such a constitution. Three such things are very hard, and if they are ever to be found together, it will be very late and after many vain attempts.

"Goodbye school" in Boy: Tales of Childhood (1984)

"The Power of Money in Bourgeois Society"
Source: Economic and Philosophic Manuscripts of 1844, p. 105, The Marx-Engels Reader