1. In Egyptian mythology, Isis was one of the most important deities. A daughter or Ra, she was the wife and sister of Osiris, and mother of Horus. She also was the sister of Nephtys and Seth. "She is featured prominently in Egyptian mythology as a goddess of immense magical power and as the archetype maternal figure. Other cultures have known her as Ishtar (Semites), Athena (Greeks), Kwan Yin (or Quan-Yin, Chinese), and Inanna (Sumerians)." (PoL) After Seth had killed his brother Osiris, Isis, with her magical powers was able to raise him from the dead.
"Perhaps the most important goddess of all Egyptian mythology, Isis assumed, during the course of Egyptian history, the attributes and functions of virtually every other important goddess in the land. Her most important functions, however, were those of motherhood, marital devotion, healing the sick, and the working of magical spells and charms. She was believed to be the most powerful magician in the universe, owing to the fact that she had learned the Secret Name of Ra from the god himself. She was the sister and wife of Osiris, sister of Set, and twin sister of Nephthys. She was the mother of Horus the Child (Hor-pa-kraat), and was the protective goddess of Horus's son Amset, protector of the liver of the deceased.
Isis was responsible for protecting Horus from Set during his infancy; for helping Osiris to return to life; and for assisting her husband to rule in the land of the Dead.
Her cult seems to have originally centered, like her husband's, at Abydos near the Delta in the North (Lower Egypt); she was adopted into the family of Ra early in Egyptian history by the priests of Heliopolis, but from the New Kingdom onwards (c. 1500 BC) her worship no longer had any particular identifiable center, and she became more or less universally worshiped, as her husband was."
[Source: Shawn C. Knight, "Egyptian Mythology FAQ" ]
2. In Earth's Galactic History, Isis is often a symbol for the Sirians. More information will be added later.