The Gravity Field Generator was a device created by Dr. Franklin Hall in the facilities of Quinn Worldwide. The device harnessed the properties of gravitonium to distort the force of gravity within a certain proximity.
After being kidnapped by mercenaries working for Quinn Worldwide, Dr. Hall was brought to Malta and approached by Ian Quinn about his work on the extremely rare element of gravitonium, which Hall had discovered and was the leading expert on. Hall was manipulated into creating the generator, which would be used by Quinn against his adversaries and establish a hold of power over his targets.
After the Malta compound was stormed by Agent Coulson's team, Coulson located both Hall and the generator in a secure room. Coulson found that Hall was sending the generator into overdrive, causing it to overheat and short-circuit. Hall had realized that both gravitonium and his research and knowledge on the element were too dangerous for anyone to have, including S.H.I.E.L.D. Successfully overheating the generator, Coulson shot a window in the lab causing Hall to be sucked into the mass of gravitonium, along with his work and research. Hall's body acted like a catalyst and stabilized the gravitonium thus stopping the generator from destroying the island.
After the generator was deactivated and Quinn escaped, the generator was sent into a secure storage vault in the Fridge. Unbeknownst to S.H.I.E.L.D, Hall still lives inside the gravitonium, existing in some fused state with the element.
The Gravity Field Generator harnessed the properties of gravitonium, which distorts the gravitational pull and attracts matter towards itself, to generate a field of gravity around a certain proximity of the generator. Depending on the intensity of power, the generator had the ability to send the force of gravity in one specific area to distort and go against its own rules, sending objects and people floating in the air, standing on the walls and ceiling and throwing them across the marked area.