Twenty years ago, on a whitewashed storefront wall in Shoreditch, London, the anonymous street artist  stenciled out a spare, innocent image: a young girl, windswept and monochrome, reaching for a bright red, heart-shaped balloon.

At the time, Banksy was still far from a household name. He was a niche artist, beloved among the taggers of the Bristol underground and increasingly notorious for the cheeky large-scale murals he produced across Bristol and London. Two decades on, he is a (still anonymous) global superstar, and that simple Shoreditch stencil has become one of the most indelible images of the 21st century.

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