David appeared as Virgin with recurring guest roles in the first season of homeland. Starting second season he became a regular.
in an interview with thinkprogress.org he said the following about Virgil:
“We discussed, prior to shooting the pilot, we had some rehearsal sessions, and there was a meeting with [writer] Michael Cuesta, [showrunner] Alex Gansa, and Carrie [Claire Danes] and we went over a lot of issues. We decided that Virgil went to the New Jersey Institute of Technology and studied engineering, and when he graduated, he wanted to work for the CIA and he applied for a job, and Saul was the guy I interviewed with, and he turned me down. And he hired somebody from MIT. So I just kind of was on my own, doing my own sort of freelance audio-visual surveillance, I met Carrie, and we became friends, and I sort of became, over time, like her big brother. My guess is, because I studied a little bit of behavioral psychology, Virgil was an outsider as a kid. And he grew up in a neighborhood in New Jersey where it was brawn over brains, and Virgil was a little bit of a tech nerd. And he was a brainiac and he had a sharp tongue, and you take a few beatings. You take a few shots to the ego and shots to your manhood, so to speak. And therefore, when you get older, you want to take care of people who are being abused or being ostracized. So it makes sense that Virgil would look after [Carrie], because she is an outsider, she is an outsider in this community. Also, everyone had someone to answer to. Saul has to answer to someone. Estes has to answer to answer to someone. Virgil has her back. Virgil’s going to look after her and take care of her. He doesn’t want what happened to him to happen to her…
As an actor, I have to justify how I’m behaving in the present. Everything we do as human beings in the present is the result of things that have happened to us in the past. People who become nurses are usually people who had to take care of their father or their mother. Archetypically, if you’re a caregiver, you’re a caregiver from a very young age. We choose these professions subconsciously.”
Sho.com describes Virgil this way:
“When it comes to surveillance, Virgil is CIA agent Carrie Mathison’s trusted resource. Virgil is a freelance operative who, along with his brother Max, assists Carrie with her surveillance needs (even if those needs are legally questionable). The compassionate and understanding Virgil shares a close, brotherly relationship with Carrie and loves her unconditionally. Virgil trusts Carrie’s judgment — but whether that trust is misplaced remains to be seen.”