It's difficult to pinpoint why Robert Gabriel Mugabe metamorphosed from champion of democracy to totalitarianism, from Marxist ascetic to uncontrolled sybarite. Power - and far too much of it - was probably a major factor.

But 20 years ago, when the Lancaster House agreement paved the way for majority rule in Zimbabwe and Mr Mugabe proceeded to win the election with a thumping majority, he expressed his unswerving devotion to "fair and just rule". He then confounded the cynics by allowing rivals into government with him and pursued a policy of reconciliation with the country's white community which had fought for so long against him.

His confidence in those early days was understandable. His party, ZANU, was drawn from the majority Shona tribe. The opposition was weak and divided. Then Mr Mugabe set about making it weaker still.

The opposition was strongest in Matebeleland, where the indigenous Ndebele tribe supported the rival ZAPU party. The army was sent in and went on the rampage for nearly two years of destruction, torture and murder. Meanwhile, the Prime Minister, as he then was, lectured the population on the merits of justice and the rule of law.

It may have been the unequal merger in 1987 of his ZANU party with what was left of ZAPU, the winning of all but two of the parliamentary constituencies and his elevation to the post of "executive President" that brought Mr Mugabe to recognise the near totality of his power. That was when the real test of statesmanship kicked in: how would he use untrammelled control and would he put the needs of the nation first?

Unfortunately, the needs of his people seemed far down the list of priorities. Priority number one for the President and his cronies was self-enrichment. Zimbabwe has an abundance of mineral and agricultural wealth. It was regarded, at the time, as a stabilising power in southern Africa when the rest of the region was experiencing great instability. Western donor nations queued to inject capital and investment soared.

But the money spawned corruption, and the road to greed and consumption was travelled at speed. Bribes became commonplace, state contracts and licences were awarded on favouritism rather than merit. The President married his secretary, 40 years his junior, and built her two mansions (one with an illegal loan from public funds) to add to his own two mansions. The First Lady then took up extravagant international shopping with shameless enthusiasm. As the President behaved, so did his flunkies.

The corruption and the flagrant accumulation of wealth by the inner circle rankled with the people, but it was the mismanagement of the economy and participation in the war in the neighbouring Democratic Republic of Congo which brought the country to its knees. Mr Mugabe has defended his extravagant military assistance for President Laurent Kabila by arguing that states must be defended from revolutionary armies, which is a bit rich considering Mr Kabila has no democratic mandate and in many ways is little improvement on his predecessor, Mobutu.

Involvement in the war is deeply unpopular, but Mr Mugabe is unmoved. When two reporters wrote about dissatisfaction with the war they were arrested by the army and tortured. The Supreme Court (still commendably independent) complained to the President about the army's behaviour and asked him - respectfully - to rein it in. He refused and criticised the court for its "impudence".

But why support Mr Kabila with the dispatch to war of 11,000 Zimbabwe troops, one-third of the army? Perhaps the reason lies in investments in minerals and timber in the Congo that Mr Mugabe's entourage has made and wants to safeguard, at all costs.

The cost to Zimbabwe has been huge - in excess of £1 million a day. The IMF and the World Bank, already incensed at the move to confiscate white-owned farms without compensation, has demanded that intervention in the war be ended; all aid has been frozen in the interim.

The country is thought to have enough foreign currency to pay for just three days of imports. It will soon be in a situation where it will be sold only what it can pay for in cash. Inflation is running at nearly 70 per cent, unemployment at over 50 per cent and there is a large budget deficit. This is an economy which urgently needs unpopular budgetary measures, but there can be no doubt the inevitable will be postponed, at least until after the parliamentary elections.

One badly needed reform concerns land. Just 50 per cent of the best arable land is owned in huge estates by 4,500 white farmers while millions of poor farmers - accounting for 70 per cent of the population - scratch a meagre living from two or three overworked acres.

But the redistribution must be fair and seen to be fair. Mr Mugabe's gamble on confiscating the lands without compensation has proved a disastrous error of judgment. He thought the domestic acclaim for such a populist measure would outweigh the international and donor community opprobrium.

Unfortunately for him, the needy farmers could remember the first redistribution of land and the fact it went, not to those who needed it but to ZANU cronies, and so they refused to support the referendum proposal. Mr Mugabe got it spectacularly wrong: damned abroad and damned at home.

He has two years left of his presidential term. On Monday he will turn 76. There is little doubt he is staring at his fin de regne. Perhaps his last judgment of significance will be the manner in which he gets off the stage: a dignified exit or an undignified manoeuvring to maintain his rule for as long as possible? Or Yeltsin-like, he may go soon if he is satisfied his hand-picked choice will succeed him and assure him of a trouble-free retirement.