Daniel is a member of the Seekers of Truth.
While investigating Caer Oswin for the missing Seekers, the Inquisitor and Cassandra come upon Daniel. He reveals that he was force-fed red lyrium, which he compares to a demon. He then reveals that Lord Seeker Lucius had betrayed the Seekers, having operated out of Caer Oswin the whole time, sending the Seekers to be captured one-by-one by the Order of Fiery Promise.
Cassandra laments that he should've joined her because he didn't support the Mage-Templar War anymore than she did. Daniel jokes that he wanted a promotion by remaining with the Seekers. Cassandra then grants him a mercy-killing to spare him any further pain.