Saul Michael Berenson is Carrie Mathison's mentor and to some extent, protector at the CIA. During Season 3 he also filled the role of Acting Director of the organization.
As of Season 7, he holds the position of National Security advisor to President Elizabeth Keane. Following her resignation at the end of the season, he is also removed from his government position. However he is re-instated by her successor Ralph Warner.
Little is known about Saul's early life yet, it has been established he majored in political science in college. He was also one of the few Jewish children to grow up in a town in rural Indiana.
Saul has worked for the CIA for 35 years. He recruited, trained, and placed Carrie in the field, and continues to have a close working relationship with her, despite not being her immediate boss anymore. He was responsible for catching Osama Bin Laden
Nick Brody's return
Carrie told Saul about the intel Hasan Ibrahim supplied regarding a turned American POW and requested permission to place surveillance on Sgt. Nick Brody, a POW who was recently rescued after long captivity. Saul denied the request, suggesting that her idea that Abu Nazir tipped off the military to the location where Brody was found was fanciful, and would need real evidence to justify action against Brody.
He did however place her in Brody's debriefing on the condition that she behave herself (which she didn't). Saul defends her against her boss, David Estes, who complained about her behavior in the debriefing, however he was warned not to let things get personal with Carrie. Saul discovered Carrie's illegal surveillance of Brody and became angry with her when she later attempted to seduce Brody. Saul does feel that Carrie justified herself when she found a rhythmic pattern in the way Brody tapped his fingers during televised appearances.
Saul becomes division chief of Europe. He is compromised due to a romantic involvement with the Berlin station chief who is secretly a Russian operative.
After Keane's election
He is tasked with the investigation of the Iranian nuclear arms deal. Eventually he finds out that a suspicious financier was a Mossad-backed operative and the Iranians stayed true to the deal.
He thinks that Javadi would convince Keane of the trustworthiness of Iran but Javadi claims that Iran would blow up the deal. Using footage of the tortured financier Keane is eventually convinced that Dar Adal wants her to distrust Iran.
Keane wants to implicate Dar Adal using the Berlin infiltration debacle but this means that Saul would be convicted as well.
After being jailed for conspiracy, Saul is brought back as National Security Advisor. Keane tasks him with bring back the fugitive O'Keefe. Eventually there is a shooting between the patriots where he is in hiding and the FBI. Saul considers this a disaster.
Saul thinks the Russians are the real source of spreading fake news reports. He reveals to David Wellington that Simone Martin is working for the Russians and is going to testify that Wellington was involved in the suspected murder of Jamie McClendon.