Paul McCarthy's huge inflatables now loom outside Tate Modern. During their construction, the artist told TATE how Blockhead was born. Photographed by Andrew Dunkley and Marcus Leith

'The initial idea for Blockhead was to make a chocolate factory to produce candy bars and a pavilion to house this factory. I first thought that the bar should be cast as a Santa Claus or Easter Bunny. It went through many forms and at one point it even ended up in the shape of a pile of shit. For the factory, an inflatable structure seemed to be a cost-effective solution. While developing this, I bought a small inexpensive plaster Pinocchio and that, finally, seemed like the perfect shape for the chocolate figurine.

'The first opportunity to make this work came with Expo 2000, the World's Fair in Hanover, where I could produce maybe 3,000 chocolate figurines a day. In the end I made Pinocchio into the inflatable and the chocolate as simple bars.

'Knowing that my model Pinocchio had some similarities to Disney's cartoon Pinocchio, I feared copyright issues. But I liked Pinocchio just as he was. I thought about putting a pipe nose on it. Then I cut off the head, dropped a block of clay on it and he was like a building, the block and the rectangle with a body in between.

'There are references in Blockhead to my earlier work. In the Sixties and Seventies I made a few minimal pieces. One is called Skull with a Tail, a cube with a tail coming out of it. (It's about Minimalism being hollow. You can't discern whether Skull is a solid cube - the box as a head - or a box over the head, like a mask. And it has no eyes. It can't see, so in a way it's either a blind head or it's a box.

'Skull with a Tail, like Blockhead, is entirely black. I have made black paintings, sculptures, black action pieces, where I'd pour black paint down a staircase or black out the windows, mirrors and doors of a house. I once made an all-black sculpture of Michael Jackson, and when installed it looked like a hole in the wall in the shape of the sculpture. I think of Blockhead as a silhouette in the landscape, a black hole in the city.

'Inflatables create attention. And they're often product-related. Big companies make brightly coloured inflatables for big events. In this case, the black Blockhead makes the object appear smaller. Blockhead's black colour tries to subvert what is attached to commercial objects like this.'