Tathag Rinpoche (Ngawang Sungrab Thutob) is also sometimes spelt as Taktra Rinpoche or Tadrag Rinpoche. He was the teacher of Reting Rinpoche as well as many others, including the previous Kyabje Ling Rinpoche. Some sources say that Reting Rinpoche nominated Tathag Rinpoche to assume the position of regent for a period of 2 - 3 years, under the understanding that power would be handed back to Reting Rinpoche after the time was up. However after 3 years, the reigns of power continued to lie in the hands of the Regent Taktra Rinpoche, who did not hand back power, triggering a series of events including the attempted murder of Taktra Rinpoche with a package bomb in the late 1940s. This culminated in the death of Reting Rinpoche in prison.
"One day, whilst I was watching a debate, I heard the sounds of shots being fired. The noise came from the north, in the direction of Sera monastery. I rushed outside, full of excitement at the prospect of doing some real work with my telescope. Yet, at the same time I was also very troubled as I realised that gunfire meant killing. It turned out that Reting Rinpoche, who had announced his political retirement six years previously, had decided to claim the Regency back. He was supported in this by certain monks and lay officials who organised a plot against Tathag Rinpoche. This resulted in Reting Rinpoche’s arrest and the death of a considerable number of his followers."
From the Dalai Lama's autobiography, Freedom in exile
When Tathag Rinpoche became the regent of Tibet, the Dalai Lama was a minor and the position of Regent was all powerful. Tathag Rinpoche remained in the position of Regent for fourteen years. And with the Chinese invasion of Tibet, power was eventually transferred to the young Dalai Lama in early November 1950
During Taktra Rinpoche's reign, the Foreign Bureau of the Tibetan Government was set up and it was also during his reign that the Chinese invasion of Tibet stepped a notch up.