Khentkaus I was probably a daughter of Mykerinos, the penultimate (?) king of the 4th Dynasty, with an unidentified queen.
Her strange titulary, mw.t nsw-bi.tj nsw-bi.tj can be translated in two possible ways: 'Mother of two Kings of Upper and Lower Egypt' or 'Mother of the King of Upper and Lower Egypt and King of Upper and Lower Egypt', the latter translation suggesting that at one point, she took up the office of king herself. This has caused some speculation about her role at the end of the 4th Dynasty and the possibility that she may have been the otherwise unattested Thamphthis who Manetho has recorded as last king of the dynasty. In this case, she would be the oldest attested queen to have used the title King of Upper and Lower Egypt.
Another interpretation of her title is that she was the mother of two kings. The story recorded on the Papyrus Westcar suggests that the three first kings of the 5th Dynasty were brothers. This story may, in part, be based on some reality. Recent research has shown that Khentkaus I was probably the wife of Userkaf, the founder of the 5th Dynasty, in which case she may have been the mother of Userkaf's two immediate successors, Sahure and Neferirkare. If this is correct, then she must have survived at least until into the reign of Neferirkare for her to be able to be called 'Mother of Two Kings of Upper and Lower Egypt'.
She was not buried in the Queen's Pyramid connected to Userkaf's funerary complex at Saqqara, but in a separate tomb at Giza, next to the causeway of Mykerinos' complex. Her tomb is neither a pyramid nor a mastaba, but has a similar sarcophagus-like shape as Shepseskaf's tomb at Saqqara. The fact that she was buried in a separate tomb points to her special status.