The alliance that he led is in the throes of a very painful transformation, one that he began and which his successor will have to complete - or see the organisation wither away. The tough German's browbeating style helped keep 16 countries with very different ideas together, but he was also one of the forces behind the revolutionary changes that have started to remake the North Atlantic Treaty Organisation.
It is easy to forget the scale of what has happened since Mr Worner arrived on 1 July 1988 at the dowdy former maternity hospital on the outskirts of Brussels that houses Nato's secretariat. The end of the division of Europe, the withdrawal of Soviet forces, and then the disappearance of the Soviet Union itself meant that in the space of five years, the landscape totally changed. And Nato forces have been in action for the first time, in Bosnia.
The main task of the alliance - the defence of Western Europe against the Soviet Union - has gone, or at least mutated out of recognition. The old saw was that Nato's task consisted in keeping the Russians out, the Americans in and the Germans down: now the American presence is vastly reduced, the Germans are 'up' and the Russians bathing on the beaches of Rimini.
There has been change, from the adoption of Nato's New Strategic Concept in Rome in 1991 to the Brussels summit this January. Seeking a new role, Nato has taken two new directions, but with uncertain results.
The first is creating new links with central and eastern Europe, or 'projecting stability to the east' as alliance officials like to call it. The Partnership for Peace scheme, launched at the Brussels summit in January, begins that task, but it is essentially designed to hold the ring.
The second new task is crisis management and peace-keeping. Recognising that it would have to look beyond the defence of western Europe, the alliance shifted its focus beyond western Europe, to a new and different kind of operation to which it is not yet well adapted. 'The slogan, out of area or out of business, is out of date,' Mr Worner told a conference last year. 'We are acting out of area, and we are in business.'
Mr Worner was bitterly disappointed by Nato's record over Bosnia, however. He believed Nato should have been called on much sooner, and should have acted more credibly and earlier. But he hated the idea of Nato as an 'errand boy' for the UN.
Mr Worner, a former Christian Democrat defence minister, was anxious that Nato should change, and often frustrated by the conservatism of some member states. But at the same time, he remained convinced of the vital and continuing importance of the alliance's central task. 'By its very existence, Nato exerts a stabilising influence around its periphery,' he said. 'The end of Nato would increase the risks of conflict in Europe dramatically.'
He was worried by the trend in transatlantic ties. It is given to every secretary-general to live with the spectre of a 'decoupling crisis,' but the longer-term trends now are not favourable to a longer-term US presence.
The secretary-general was also concerned by trends in defence spending, warning publicly on several occasions that cuts were happening too fast, in an unplanned way and without much thought.
Though Moscow is increasingly tied to the West, Mr Worner, an old hawk at heart, remained highly suspicious of Russian intentions. Plans to remake European security under an 'umbrella' organisation like the Conference on Security and Co-operation in Europe raised hackles in Brussels, as did Russian attempts to negotiate a 'broader dialogue' with the West when it signed a PFP deal. The formula that emerged - no vetos, no surprises - shows the fragile nature of the relationship.
Mr Worner's successor will have to confront all this and more. On the horizon is a larger role for the European countries, through the Western European Union. At Nato headquarters, budgets are falling, manpower is stretched and old-timers are resisting reform while outside critics want faster change. It will not be an easy job.Reuse content