Which architect's Sagrada Familia was still unfinished a century after his death?

Gaudí's. He took over the project in 1883, spent the last dozen years of his life on nothing else, living on site, and was run down by a tram in 1926 - so shabby by then that he was taken for a beggar and left in a pauper's ward for a day before anyone recognised him.

He worked without conventional drawings. The structure was designed with hanging chain models loaded with weights: a chain under gravity takes the ideal shape for a load in pure tension, so photographing the model and turning it upside down gives the ideal compression arch. That is where the leaning columns and branching interior come from - they are not decoration, they are the load paths, and they let the building stand without the flying buttresses he called crutches.

The original models were smashed in the Spanish Civil War, so the continuation has been reconstruction as much as construction, argued over ever since by architects who think the whole thing should have been left as a ruin. Work sped up enormously once computer modelling and stone-cutting machinery could handle the geometry, and it is now expected to be structurally complete around 2026, a hundred years after he died.