Ions (1968:54) hypothesizes that the cult of Osiris was originally brought to Egypt by Syrians (probably in predynastic times) as they settled in the delta town of Busiris, where the god Andjety was the dominant local god. There, it appears that Osiris was given the royal regalia (crook and flail) of Andjety and was worshipped as a local god of fertility, responsible for the success of crops. From these humble beginnings, Osiris rose to become one of the most prominent gods in the Egyptian pantheon.
By the end of Dynasty 5, the cult of Osiris may have reached such a level of popularity that the priests of Heliopolis, who up to then enjoyed complete control over national theological doctrine, felt a need to take counter-measures to remain in control of this newcoming god. Instead of trying to suppress him, they incorporated Osiris in the family of the solar god, limiting his prestige by making him a great grand-child of Atum. If their aim had been to curb the expansion of the Osirian cult, they were less than successful. Orisis would keep growing in importance by associating with other deities, eventually absorbing their powers and prerogatives.
"… his earliest appearance yet attested [is] on a block from the reign of King Izezy [Djedkare Izezi, penultimate king of Dynasty 5] which shows the head and part of the upper torso of a god, above whom are the hieroglyphic symbols of Osiris’s name" (Hart 1986:151). But depictions of Osiris remain rare until Dynasty 12 (Budge 1973:[1]31).
In earlier dynasties, the traditional dogma was that the king became a god—the God Horus—upon his coronation, then joined the God Re in his solar ship upon his death, and sailed the firmament for eternity. The next king would in turn become Horus. At some point during dynasty 5, the dogma changed radically, calling for the deceased king to become Osiris upon his death. Not only had the cult of Osiris reached national recognition, but it had become part of the very nature of kingship. Although this relationship between king and Osiris was a new development, the Egyptians sought to make it appear original. Indeed, the legend of Osiris places him as the ancestral king of Egypt.
There is some evidence that Old Kingdom kings were not completely at ease with this new tradition. "… sentiments can be found that reveal an apprehension or dread of the ruler of the Underworld. This reflects the underlying desire of the monarch to be with the sun-god in the sky as a visible phenomenon, rather than to dwell in the unknown and forbidding regions of Duat" (Hart 1986:154).
With the general ‘democratization of death,’ Middle Kingdom Egyptians started aspiring to become Osiris, like their king. But as earlier with kings, this hope remained tainted with dread. Osiris exerted on Egyptians an ambivalent fascination, commanding a respect that was partly rooted in fear and even disgust—"… in the Middle Kingdom, there exist in the Coffin Texts descriptions of Osiris that conjure up a picture of a threatening demon. He glories in slaughter, utters malignant spells against a dead person, and runs a ‘mafia’ consisting of executioners called ‘Osiris’s butcherers painful of fingers’ or ‘Osiris’s fishermen’" (Hart 1986:155). Ref. www.virtual-egyptian-museum.org