Emeritus Professor of Law of the Universities of Leiden and the Witwatersrand and former Director of the Lauterpacht Centre for International Law, Cambridge. He participated in the drafting of South Africa’s democratic Constitution of 1996. He was a member of the International Law Commission (1997–2011) and Special Rapporteur on the subject of diplomatic protection, the UN Special Rapporteur on the Situation of Human Rights in the Occupied Palestinian Territory (2001–2008), and Judge ad hoc of the International Court of Justice (2000–2018). He has taught at the Hague Academy of International law and has published several books and many articles on international law. He is a member of the Institut de Droit International and an Honorary Member of the American Society of International law.