Lady Justice is an allegorical personification of the moral force in judicial systems.
The personification of justice balancing the scales of truth and fairness dates back to the Goddess Maat

Maat

Maat is a naval rank of the German navy equivalent to the army rank of Unteroffizier. A Maat is considered the equivalent of a junior Petty Officer in the navies of many other nations....

, and later Isis

Isis

Isis or in original more likely Aset is a goddess in Ancient Egyptian religious beliefs, whose worship spread throughout the Greco-Roman world. She was worshipped as the ideal mother and wife as well as the matron of nature and magic...

, of ancient Egypt. The Hellenic

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

 deities Themis

Themis

Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law, and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the verb τίθημι, títhēmi, "to put"...

 and Dike

Dike (mythology)

In ancient Greek culture, Dikē was the spirit of moral order and fair judgement based on immemorial custom, in the sense of socially enforced norms and conventional rules. According to Hesiod In ancient Greek culture, Dikē (Greek: Δίκη, English translation: "justice") was the spirit of moral...

 were later goddesses of justice. Themis

Themis

Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law, and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the verb τίθημι, títhēmi, "to put"...

 was the embodiment of divine order, law, and custom, in her aspect as the personification of the divine rightness of law.