“Law is king of all.”

The Tale of Despereaux (2004)

Act II, scene i.
Bussy D'Ambois (1607)

De pareils serviteurs sont les forces des rois,
Et de pareils aussi sont au-dessus des lois.
Tulle, act V, scene iii
King Tullus forgives the hero, Horace, who has saved the state but killed his sister.
Horace (1639)

Epilogue to the Code of Hammurabi (translated by Leonard William King, 1910). i like potatoes

So it has always been with tyrants among our own people: when the King was tyrant, let him look out. And it has always been the same, and will be the same, whether the tyrant be the Barons, whether the tyrant be the Church, whether he be demagogue or dictator — let them look out.
Speech at Westminster Hall (4 July 1935); published in This Torch of Freedom: Speeches and Addresses (1935), p. 4
1935

Prohibitions del Roy, 12 Co. Rep. 63, quoting Henry de Bracton's treatise on the laws and customs of England. http://www.uniset.ca/other/cs4/77ER1342.html
Institutes of the Laws of England

Bk. 7, line 2695.
Confessio Amantis

The Revenge of Bussy D'Ambois (1613), Act IV, scene i.

Ogni giusto re primo servatore dee essere delle leggi fatte da lui.
Seventh Day, Tenth Story
The Decameron (c. 1350)