Short answers, pulled from the story.
Isis was a major goddess in ancient Egyptian religion first mentioned in the Old Kingdom, around 2686 BCE. She was central to the Osiris myth, in which she resurrects her husband Osiris, protects their son Horus, and uses her magical power to govern fate and the natural world. Her worship eventually spread across the Greco-Roman world.
The name Isis derives from the Greek form Ἶσις, itself based on the Egyptian name ꜣst, whose pronunciation shifted over centuries from Rūsat to ʾĒsə to the Coptic Ēse. The hieroglyphic writing of her name incorporates the sign for a throne, leading Egyptologist Kurt Sethe to suggest she was originally a personification of thrones, though other scholars dispute this interpretation.
The cult of Isis spread beyond Egypt during the Hellenistic period, following the conquests of Alexander the Great in the late fourth century BCE. Merchants and travelers established Isis and Serapis cults in Greek port cities at the end of the fourth century BCE. The cult reached Italy in the second century BCE and, at its peak in the late second and early third centuries CE, was present in most towns across the western Roman Empire, from Londinium in Britain to Petra in Arabia.
The Navigium Isidis was a festival held each March celebrating Isis's influence over the sea and serving as a prayer for the safety of seafarers and the Roman people. It consisted of an elaborate procession of Isiac priests and devotees carrying a model ship from the local Isis temple to the sea or a nearby river. Listed on Roman calendars as early as the first century CE, the festival lasted well into the sixth century.
The question is contested among scholars. Some customs of the Isis cult, including personal devotion to a single supreme deity and an initiation rite, resemble Christian practices, but scholars Hugh Bowden and Jaime Alvar argue these similarities stem from a shared Greco-Roman cultural background rather than direct borrowing. Parallels between Isis and Mary, the mother of Jesus, including shared titles such as "queen of heaven" and nursing iconography, have been debated for more than 200 years without a settled answer.
The temple of Isis at Philae was the last fully functioning temple in Egypt. Supported by its Nubian worshippers, it maintained an organized priesthood and regular festivals until at least the mid-fifth century CE, long after most other Egyptian temple cults had ended due to lack of funds and Christian hostility.