Sothis (Greek Σῶθις) is the name of a star that the Egyptians considered unusually significant. The star is not explicitly identified, but there are enough clues for modern scholars to be almost unanimous in identifying Sothis as Sirius.
Prof Karl Kerenyi claims an ancient mythic figure Iachen (or Iachim) represents a sublimated form of Sirius or Sothis. Sirius rose with the Nile flood and was also associated with epidemics, Sothis was thus a destructive and greatly feared goddess (perhaps akin to Sekhmet, or an Egyptian equivalent of Kali). Iachen was said to be an Egyptian magician who 'tamed' the power of Sirius and transformed it into a life giving power (just as the flood fertilised the land of Egypt with fresh Nile mud). When he died he became the centre of a cult which kept a flame burning on his altar. When Sirius rose the priests of Iachen entered the streets with torches lit from the altar, in order to channel the power of Sirius and heal any diseases unleashed by it. Iachen was known in Minoan Crete as I-wa-ko, who became the Greek torch bearing son of Persephone - Iakchos, who was also associated with Sirius, as ‘the light bearing star of the nocturnal mysteries’ according to Kerenyi. The late Isis took on the role of many more ancient deities, including Neith, Hathor and the lion headed Sekhmet.
The connection between Sirius and a dog may reflect the stars association with the destructive power of the goddess, universally symbolised by various predators of feline or canine origin (lions, tigers, panthers, wolves and hunting dogs in particular). In Greek culture this became the she-dog of Orion, the sublimated form perhaps. Gods who ride such animals, notably Shiva and Dionysos, or who have canine servants, notably Orion and Osiris (with Anubis his gatekeeper and embalmer), were also regarded by Kerenyi as partly derived from Iachen, the sublimator, or an even older myth. Dogs associated with various incarnations of Dionysos, as well as with Orion's dog (Sirius), were regarded as the discoverers, or bearers, of the first grapevine, this was probably because Sirius rose in the period of the vines blossoming, shortly before harvest. It also reached its highest point in the sky on around Jan 1st, just before the birth of Dionysos on Jan 6th (epiphany), associated with the opening of the first wine.
The universality of Sirius lore, even the Pawnee tribe of North America, and others, referred to Sirius as the 'Wolf Star', indicates this Sothic Mythos may have extremely ancient roots, perhaps as old as the first humans to migrate from Africa.