A series from Chris Carter, who is better known for creating The X-Files. It starred Lance Henriksen as Frank Black (no, not the singer). He was a former FBI agent who joined a sort of secret society called the Millennium Group, which consisted of other former police and federal agents and such. Frank was married to a clinical social worker named Catherine (Megan Gallagher, of whom I was a fan from Nowhere Man). They had a daughter named Jordan. The only other character I remember at all is Peter Watts (played by Terry O'Quinn, whose work I'd later enjoy on Lost), another member of the Millennium Group.
The show ran for three seasons, from 1996-99, but I didn't see all of it, and I don't clearly remember what I did see. I believe the Millennium Group were aware that the end of the world was coming, or something, and so there was lots of evil going on... but then, that had been going on for like a thousand years, so... I dunno. I really want to see the whole series someday and write a proper review, and see if I can figure out what it was all about. The show had supernatural elements, mysterious elements, law enforcement elements... so I'm not sure how best to classify it. But it was definitely a very dark and depressing show, and there was this sense that no matter what Frank, the Millennium Group, or anyone did, ultimately things were basically hopeless. Still, they did what they could. Though there were also some opposing factions within the Group, and Frank eventually left, I guess. I don't know what else to say, right now.