Who is Gurpatwant Singh Pannun, Khalistani separatist believed to be the brainchild of Pakistan's ISI?

Gurpatwant Singh Pannun assassination plot: After the US department charged an ex Indian intelligence officer in a failed plot to kill Gurpatwant Singh Pannun, the Khalistani separatist is back in the news again. Pannun, born in Punjab, has dual US-Canada citizenship and is believed to be the brainchild of Pakistan's ISI. He is a wanted terrorist in India.