George Odlum, who has died aged 69 of cancer, was a key figure in the Anglo-Caribbean "new left" movement that rattled the Reagan administration and led to the 1983 US invasion of Grenada. He also did more than anyone to arouse the people of his native St Lucia from the colonial torpor weighing on the island when Britain thrust independence on it in 1979.
But his taste for squabbling with allies, coupled with the fear he inspired in local elites and in Washington, ensured that when he did gain office, he remained forever second fiddle to politicians whose more parochial vision he could rarely stomach.
Born in St Lucia's capital, Castries, one of 14 children of a barber, Odlum belonged to the small band of Anglo-Caribbean radicals - modern-minded, foreign-educated, middle-class graduates - who fired up the region in the 1970s in the wake of the US "black power" movement and the Vietnam war.
With an economics degree from Bristol University (where he was the first black student union president in 1958) and then Oxford University, the ever mournful-looking Odlum went home to a job in the trade ministry. But he was soon back in London to take up a more rewarding post with the Commonwealth Secretariat.
In 1967, as the eastern Caribbean islands moved to pre-independence self-rule, he became executive secretary of their grouping, the West Indies Associated States. "Black power" riots in Jamaica, in 1968, and uprisings in Curaçao and Trinidad galvanised the region's new intellectuals.
In 1970, Odlum organised a secret conference of their leading lights, including the later-martyred prime minister of Grenada, Maurice Bishop, on Rat Island, just off St Lucia's main tourist strip, where the demeaning level of local control enraged the socialist ideologues. They returned home to launch "Forum" groups to educate their compatriots about the local and foreign forces they saw obstructing true national feeling, prosperity and regional unity.
In 1972, Odlum founded the St Lucia Action Movement (SLAM), which shunned the Westminster electoral system. But a year later, he merged it with the enfeebled mainstream opposition St Lucia Labour party (SLP), and set about reinvigorating it, as a means to win power.
"Brother George", as the talented orator came to be known, made his base among the island's small farmers, who produced the bananas that were then its chief resource, and led frequent strikes to improve their conditions. His campaign against robber-baron terms, demanded by the US oil transnational Amerada Hess for building a giant tank-farm on the island, also made him a local hero.
His enemies pointed instead to his enthusiastic links with Cuba and Libya. In July 1979, four months after Bishop seized power in Grenada and five months after St Lucia's independence, Odlum's efforts swept the SLP and its elderly figurehead, Allan Louisy, into office at elections, ousting the tired regime of prime minister John Compton.
Under pressure from panicked US officials and their local allies, Louisy at once reneged on his secret promise to hand over the premiership to Odlum within six months. A furious Odlum complained loudly, which made him seem undignified and petty.
Louisy sacked him as his deputy, the SLP broke apart and three, often-farcical, years of infighting and government paralysis ensued. His fellow regional radicals privately felt his theatrical behaviour was damaging their cause. Voters returned Compton to power in 1982 and Odlum lost his parliamentary seat. He took his revenge on the SLP in the 1987 election when his new Progressive Labour party split the vote and deprived it of victory.
In 1995, after 13 years in the wilderness, during which he alternately harangued, enlightened and entertained St Lucians through his newspaper, the Crusader, he accepted the job of UN ambassador from his old enemy Compton. He then helped the SLP regain office in 1997, was re-elected to parliament himself and named foreign minister, only to be sacked in 2001 after secretly allying himself with Compton again.
Such opportunism tarnished his final years, but on the day he died thousands of people, including government leaders, gathered in the island's capital for an emotional pre-planned rally to honour him.
He is survived by his ex-wife Fleur and four children.
· George Odlum, politician, born June 24 1934; died September 28 2003