Robert Bitker was born in the Russian Empire, migrated to China and was Betar commander in China. Bitker was commander of the Jewish military unit in the international zone in Shanghai with the rank of colonel.
Bitker immigrated to Eretz Israel in 1937 and joined the Irgun General Headquarters. After Avraham Tehomi, commander of the Irgun, returned to the Haganah ranks, Bitker was appointed Irgun Chief Commander. He was deposed soon afterwards because of his involvement in the robbery of Irgun member at the Poalim Bank, and emigrated to the United States, where he lived till his death.
Sources: The Irgun Site