It’s theorized that he is Taniks, due to the reddish color scheme and vaguely similar helmet shape. Additionally some of the community noted that there are motifs in the track that are from Taniks. Something I noticed is that if the team wipes it’ll say in the corner that he celebrates your defeat - which seems to suggest he has a vendetta against you. The overall reason people theorize he is Taniks reshaped by the Witness - is that it is a subtle nod to the running community joke that Taniks would be the final boss of the raid, due to his nature of returning multiple times despite his supposed deaths. Maybe Bungie will release lore on him later, revealing the true identity, or just continue to leave it to our imaginations.