DEFEND is the Department for the Enforcement of Extraordinary National Defense is a top secret government paramilitary organisation. Their brief is to protect the nation from all treats related to super-humans, super technology, alien and mystical threats.
Their agents are highly trained, and equipped with cutting edge technology (much of it reverse engineered from tech captured form super villains and aliens). They are skilled at identifying weaknesses and exploiting them, as well as containing captured super-powered individuals. While an individual agent might be no match for a powerful superhuman, their sue of tactics and team work mean they can overwhelm most superhuman threats.
They are well funded, channeling resources from the government 'black-ops' budget. Their existence is not well know, even in the highest circles of power, and many of those who do know about them question who exactly leads them, and who they are accountable to.