The seat of power in Bill Gates's empire occupies the top floor of an anonymous suburban office block overlooking Seattle's Lake Washington. Here, in the inner orbit of the second richest man on earth, everything – down to the modern artwork and screens embedded into the walls, to the gleaming staff canteen replete with a faux wood-burning stove – is curated to the utmost precision.

No more so than the man himself, whose daily schedule is managed by assistants into five-minute chunks. When Gates arrives for our interview in his glass office, nicknamed "The Fishbowl", he cuts an immaculate presence, tall and surprisingly suave in dark trousers and slate grey cashmere. The only blot is a marker pen smudge running the length of his left palm, presumably from scrubbing furiously at some white board earlier that day. Even in the 62-year-old Microsoft founder's second life as the world's philanthropist-in-chief, the old number-cruncher dies hard.