ALEX Salmond is one of the most significant Scottish - indeed British - politicians of the past three decades.

Of course it didn't appear that way at first. As the leader of just three MPs in the House of Commons in the early 1990s, the "young Robespierre" as Sir Malcolm Rifkind dubbed him was seen as a talented yet unthreatening fringe politician.

But Mr Salmond was content to play the long game: broadening support for not just the Scottish National Party but, along with it, independence and, of course, displacing Labour as Scotland's main left-of-centre party.

It took time, lots of time, and in the interim he resigned as leader of the SNP. As it did yesterday, his resignation came as a surprise. Remarkably, he was leader of the SNP - on and off - for one quarter of a century, a feat unrivalled in the UK and perhaps the Continent. Mr Salmond redux was more impressive, although the ground work laid during his first decade at the helm (1990-2000) proved invaluable.

During that period he made the economic case for Scottish independence credible. Drawing kudos from his career as an economist with the Royal Bank of Scotland (although in reality he was more of a PR man), Mr Salmond spoke the language of business with ease, while also looking the part - although ostensibly a left-wing radical in his youth, by the 1980s smart double-breasted suits were de rigeur. His aim was to make the SNP and its raison d'etre respectable, much as Ramsay MacDonald laboured in the 1920s to reassure voters that socialism needn't disrupt their lives (at least not too much).

Two decades later this strategy reached its natural culmination when Mr Salmond made that pitch direct to voters. Independence, he argued with remarkable ease, will transform your lives but with minimal disturbance to the status quo.

It was a very conservative vision of Home Rule, designed not to scare the horses. The European dimension ("independence in Europe") was conceded early on, followed by sterling (previously a "millstone"round Scotland's neck) and Nato (a long-standing tactical boil only lanced a few years ago).

Mr Salmond's strengths were tactical and strategic rather than philosophical. He was not a politician easily distracted by abstract ideological or political consistency. He spent decades patiently cultivating support in sections of Scottish society previously hostile to the SNP (and independence), such as its Catholic and Asian communities.

He was never a great policy man (although energy was an important exception), his guiding philosophy being "whatever works", much as it was Tony Blair's, a contemporary he usually derided: the professionalisation of his party, skilful cultivation of the media and the adoption of free-market economics under the rhetorical guise of "social democracy". Unlike Mr Blair, he derived economic inspiration from the "Celtic Tiger" model pursued by Ireland , which included cutting Corporation Tax.

Mr Salmond's theatrical side would certainly rise to the occasion in oratorical terms and digest a brief (his memory is prodigious, verging on photographic), although he was generally over-rated as a debater. His main preoccupation was political bloodsport.

Personally, to paraphrase Walt Whitman, Mr Salmond was large (though that changed in recent years) and contained multitudes. Capable of immense charm and thoughtfulness, he could also be a bully, intolerant of his aides' inadequacies or journalists' impertinence. For all that, he was a big beast, so much so it's difficult to conceive of a Scottish political stage deprived of his presence.