I only have one atm. The father of Anna's daughter, ex DPA gone rogue.
To get the specifics it'll be worth looking at Anna's and Grace's bios but basically the only a couple of musts: is that he's American, was on secondment in the UK to train with the DPA which is where he met Anna. He went rogue and is currently working with the Nahash. He is presumed dead by the DPA.
The play by can be changed, I always imagined him looking like Ben Browder