Harry Harrison has died. When I was going through my phase of devouring SF books during my teens and twenties, he was one of my favourite authors. On one level, his books could be read as action tales, but there was usually a serious underpinning. So Deathworld was underpinned by Darwinian selection, Bill, The Galactic Hero by an almost Swiftian satire, and Make Room! Make Room! by the question and consequences of human overpopulation.
But I think my favourite of his novels remains Captive Universe, which opens with a heartstopping sequence (quite literally) in an apparently Aztec setting. It develops into a thought-provoking tale about colonisation and eugenic control. Well worth reading.