Daeva

Daeva are malevolent creatures are were the ones opposing the Titans in the War of the Ancients. Although wiped out, as long as there is evil in the world more of them are born. Due to the Angles influence they are commonly referred to as Devils.
Angels miss-interpreted the titan word for Daeva as Devil which lead to them referred as such.
While most of them were evil, some Daeva's switched sides and fought alongside the Titans, the Titans referred to them as the Adrestia and they were allowed to do anything a Titan could do, but were secretly monitored.