Original: UN secretary-general Thant began serving as acting secretary-general from November 3, 1961, when he was unanimously appointed by the General Assembly, on the recommendation of the Security Council, to fill the unexpired term of Dag Hammarskjöld.
Simplified: UN Secretary General Thant began serving as Acting Secretary-General from November 3 1961, when he was unanimously appointed by the General Assembly, on the recommendation of the Security Council, to fill the unexpired term of Dag Hammarskjöld.