Gavriel was born on January 14, 1914 in Izmir, Turkey to Aharon Mordechai and Sarah. The family made aliyah in the 1920’s illegally, taking a ship to Beirut, then smuggled by way of Rosh HaNikra via Nablus to Jerusalem.
They then moved to Neve Zedek in Tel Aviv. His father worked in the film industry, representing Paramount Studios.
Gavriel finished his schooling at the Alliance (Kiah) School and the commercial high school. After finishing his studies, he started working in his father’s office. In 1936, at the time of the riots, he joined Hagana and guarded the border of Tel Aviv from the Arab rioters. From the Hagana he moved on to IZL, and he took part in anti-Arab attacks such as bombing the railroad, et cetera. Once IZL split, Lehi was his and his brothers’ choice. His family, which supported the underground, allowed Yair, whom his father knew from his travels abroad, to use their house at 89 Dizengoff in Tel Aviv.
He used his travels abroad on business to pursue the interests of the underground. Gavriel took part in the operation to rob the Arab bank in Jerusalem in 1941. According to Yair’s command, he contacted a French officer in Lebanon to get weapons for the underground. After Yair’s murder, he continued to serve in Lehi under Yitzhak “Michael” Shamir and Natan “Gera” Yellin-Mor. His home on Hisin Street in Tel Aviv was a Lehi headquarters and hideout for Gera.
In 1942, he married Flora Costi, and they had two children and numerous grandchildren.
When the State was established, he joined the 8th Brigade, like other Lehi members, under Yitzhak Sadeh. He was secretary for the command staff of Battalion 82 as it fought throughout the central and southern regions of the country.
After the war, he went back to work in the film industry.