Short answers, pulled from the story.
Themis is the Greek goddess and personification of divine order, justice, and law. She is one of the twelve Titan children of Gaia and Uranus, and the second wife of Zeus. By Zeus, she became the mother of the Horae (the Seasons) and the Moirai (the Fates).
The name Themis means "divine law," literally "that which is put in place," from the Greek verb títhēmi, meaning "to put." The scholar Moses Finley called the word "untranslatable," noting it could mean right custom, social order, or simply the will of the gods.
Themis built the Oracle at Delphi, according to one tradition, and was herself oracular. A second tradition holds that she received it from Gaia and gave it to Phoebe, who passed it to Apollo as a birthday gift. Ephorus also recorded that she helped Apollo find the oracle site with the intent of helping mankind.
By Zeus, Themis was the mother of the Horae: Eunomia (Law), Dike (Justice), and Eirene (Peace), and also of the Moirai: Clotho, Lachesis, and Atropos. In Prometheus Bound, attributed to Aeschylus, she also appears as the mother of Prometheus.
In modern depictions, Themis is most often called "Lady Justice." Classical descriptions depicted her as a sober-looking woman holding scales or a sword. In 2022, the building hosting the main courtroom of the Court of Justice of the European Union's General Court was renamed the Themis Building.
When Themis is disregarded, Nemesis brings just and wrathful retribution in her place. The two goddesses shared a small temple at Rhamnous. Themis represented the principle of divine order while Nemesis carried out the consequence when that order was violated.