Devro was a citizen of the Hierarchy.
He was second in command to Phlox during a reconnaissance mission to find ships that were easy targets for boarding to steal technology. Devro and Phlox mistakenly interfaced with The Doctor's matrix and believed what they were seeing was reality. In fact, what Devro was seeing was The Doctor's daydreams.
When Phlox presented his findings to The Overlooker, Devro warned Phlox that he was too confrontation, and that the Overlooker might report him.