Eighty-eight-year-old Jack Bogle is something of a pin-up. The ageing investment guru who launched the first-ever index fund in 1976 has many admirers — in fact, he has his own giant fan club, the 50,000 members of the Bogleheads internet forum who lovingly debate and dissect the New Jersey native’s low-cost investment philosophy.

One particular Bogle devotee stands out: Billionaire investor Warren Buffett, who in his annual letter to shareholders produced a remarkable volley of tributes.