As per the today’s widely accepted assumptions, the pyramid of Menkaure was probably completed in the 26th century BC. Pyramid of Khafre was built during the reign of Khafre who ruled from 2558 to 2532 BC. The great pyramid of Khufu was built during 2580-2560 BC.
These dates are acknowledged by Dr Zahi Hawas as well, who is director of archeology department of Egypt, and holds the supreme command in ancient Egyptology (His team’s recent achievement is discovery of mythical tomb of Osiris, god of the Dead in ancient Egypt. That was truly a waooo news for me, and all other readers)
Another group of researchers claims something else. According to Robert Bauval, The Giza pyramids are a Stellar representation of Orion’s Belt (a well-known constellation of our Milky way galaxy). In his “Orion correlation theory“, he states that the three pyramids of Giza are exact mapping of three stars in Orion constellation. The location & distance in between of pyramids represents three stars, whereas the milky way was associated with river Neil. As per his theory, this mapping was happened in 10th millennium BC, hence pyramids were built much much before the Egyptian civilization. (watch the BBC documentary which is well convincing on this this topic).
So the dates and actual builders of these pyramids are still a mystery (atleast for me). Archeology department of Egypt government has official statements thats pyramids were built during 2700BC to 2500BC by the rulers of that time.