Sam Deker is an agent with the Israeli Shin-Bet.
We initially meet Deker towards the end of an adventure dealing with astro-archaeologist Conrad Yeats and his sometimes partner and colleague Serena Sergetti, helping to resolve a very nasty situation those two had gotten involved with; though that pair do not make any repeat appearances in the adventures dealing with Deker.
In that first meet, we are told a good amount about Deker and his affiliation with Israel's internal security service: "A secular Jew who had grown up in Los Angeles and served with the U.S. armed forces as a demolitions specialist in the wars in Afghanistan and Iraq, Deker had been recruited by the former head of Israel's internal security service, Yuval Diskin, to work for the Shin Bet. A man who specialized in the destruction of major structures, Diskin told him, was uniquely qualified to protect one such as the Temple Mount. However, Deker quickly gathered that his chief qualification was that he was Jewish but not a real Jew, if that was possible."
That last part is particularly interesting and important in the case of Deker as we are told in the first adventure dealing primarily with him. As that mission begins, we are reminded that this 26-year-old man was a secular American Jew who might carry the Jewish lineage inside him but who was not at all religious - hence Jewish but not a Jew.
Deker had had no intentions of being in the counter-espionage business nor even the military when he was growing up. His career path changed as he was just becoming a man, joining the U.S. Army after his father was killed in the Twin Towers and then graduating at the top of your class at West Point. He would extend his training to become a Ranger, though he got into considerable trouble when he went after bin Laden on his own. A request for assistance by the Israeli Defense Force put him into that country for a time and while there, he was notices by Shin-Bet and recruited.
The adventures that Deker will take part in after we meet him will start out exciting and interesting but still grounded in the normal. After that, however, things do start to get a bit bizarre and not more than once does Deker have to question his own sanity.