Nephthys is almost universally depicted as a woman with the hieroglyphic symbols of her name (a basket and a house, stacked on top of each other) situated atop her head, though she can also be depicted as a bird (most often a kite or some other form of falcon/hawk). She was associated with funerary rituals throughout ancient Egyptian history and was venerated not as Death itself, but as the companion who gives guidance to the newly deceased, and as a Lady With Wings who comforts the deceased's living relatives. Nephthys is in most myths the youngest daughter of Nut, sister of Isis and Osiris and the sister-consort of Seth. In later periods Nephthys is also considered to be the mother of Anubis, a primordial form of the lord of the dead who later became subservient to Osiris in the Egyptian cultic myth.
Nephthys had connections with life as well as death -- she stood at the head of the birth-bed to comfort and assist the mother giving birth (while her sister, Isis, stood at the foot to midwife the child).
To our current Egyptological knowledge, Nephthys did not have her own cult or temples in Egypt until the Ptolemaic-Roman period; however, as her name is merely a title (the same title given to the eldest woman in any ancient Egyptian household), it is possible that Nephthys may be a specialized form of another goddess; probable candidates include Bat (as she is called the "Lady of Het," or "Nebt-het") and Neith (with whom Nephthys is paired in the canopic shrine quadrants, as Isis is with Serket, who is sometimes seen to be an aspect of Isis.
Neith's being the "eldest of goddesses," along with her connection with weaving and funerary garments lends credence to this theory, as does the interchangeable depiction of Neith and/or Nephthys in symmetrical transposition on a number of Late Period temples.