THE second secretary general of the United Nations, Dag Hammarskjold, died 50 years ago this weekend on a mission to the Congo, when his plane crashed on its landing approach to Ndola, now in Zambia, then Northern Rhodesia. In his eight years at the United Nations, he brought vitality to the world organization and established its secretary general as a major player in global affairs.

Hammarskjold’s resolute international leadership has never been equaled. He developed the role of the secretary general at a particularly dangerous point in history to such a degree that “Leave it to Dag” became a slogan, even as he ran the risk of arousing the ever-vigilant defenders of unlimited national sovereignty. The men who succeeded him (when, at last, will a woman be nominated?) have often been measured against Hammarskjold, and they have referred to him as a model for their own efforts.

When Hammarskjold arrived at the United Nations in April 1953, most of the members of the Security Council were under the impression that they had voted for a competent Swedish civil servant who would not rock the boat or be particularly active or independent. The next eight years were quite a surprise....

The Security Council has recommended, and the General Assembly has approved, a second five-year term for Secretary General Ban Ki-moon. But the process of finding his successor by an imaginative, widespread search procedure should start soon. In a time of ominous global problems, the example of Dag Hammarskjold could provide important guidance in that search.