Forerunner (Halo)

The forerunners are the ones who created the seven Halos that exist all over the Milky Way Galaxy, in order to study and contain  the Flood, and in case of an outbreak, activate Halo´s defenses and kill all  sentient life in the galaxy to starve them to death. They´re believed to be extinct because they were forced to activate Halo to stop an outbreak, much earlier in history; of course, it is unknown whether or not if they in fact perished with the halos' activation or not.

Location of Installation 00
While some believed that Installation 00, also known as "the Ark", was buried under New Mombasa in Africa, this turned out to be false; instead, a Keyship lay there, which in fact was built to open up a portal leading to the Ark. The existence of this Keyship on Earth and Master Chief being called a "reclaimer" indicates some connection between  Humans and Forerunners. While it is known that one Forerunner did discover Earth and its not-yet-sapient species, it is unknown at this time what, if anything, that Forerunner might have done to affect the Human race's evolution. As for the Covenant, the Prophets and their lackey Tartarus know something, which they chose to keep from both the Humans as well as the other Covenant races:

From the event of Halo 3 and the information given from the Besterium, the humans are indeed forerunners or at least genetically related to them. The reason why the Prophets tried to eradicate the human race was because the existence of the humans caused flaws in their religion. This was because according to their religion, all the forerunners ascended to a greater plain of existence via the halos.If the still existent via present day humans, then their belief would be flawed.