Can it really be more than 20 years since a young conductor by the name of Valery Gergiev swept into the UK on a wave of glasnost and proceeded to launch a stealthy invasion that has taken him to the top of British musical life?

Not for the first time, this summer’s music calendar has Gergiev written all over it. He is the face of the Edinburgh International Festival’s classical and opera bill, bringing the London Symphony Orchestra to Scotland for a Prokofiev cycle as well as his own Maryinsky Opera Company for no fewer than four operas.

And yet it has been a rollercoaster ride. Some visits with the Maryinsky, dynamic in the Russian classics but iffy when trying to innovate, have been unforgettable for all the wrong reasons; flickering through the adulation of his world-beating Tchaikovsky, Prokofiev and Shostakovich interpretations have been the distinctly cooler responses when he has tried to broaden his range.

Few would deny that pleasure has outweighed pain. When he’s on form, those spidery fingers are electrifying and his performances red-letter evenings. And perhaps the excitement comes about precisely because of the dangerous ambiguity.