A Lord of Chaos is a powerful magical being, and the ultimate enemy of any Lord of Order. Lords of Chaos want to destroy all order and make the world fall into the control of chaos. A Lord of Chaos is an extra-dimensional being; in order to manifest in the physical realm, they have to be anchored by a host or through a familiar.
It is impossible to stop or even contain a Lord of Chaos, because they are chaos incarnate. Thus, even Doctor Fate stresses that it is futile to try to kill or capture one. The most that can be done is to foil their plans for chaos and defeat them temporarily, but chaos is an eternal force in the universe and will always rise another day.