H.G. Wells The War of the Worlds (1898)
Speaking of iconic opening lines - if iconic is really something that can be applied to text, which it possibly may not be - The War of the Worlds just about trumps any other novel I can think of right now:
No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intelligences greater than man's and yet as mortal as his own; that as men busied themselves about their various concerns they were scrutinised and studied, perhaps almost as narrowly as a man with a microscope might scrutinise the transient creatures that swarm and multiply in a drop of water.
And it just keeps getting better from thereon, which isn't bad going for a novel with a plot which can be summarised in a single short sentence - proof, as if it were needed, that the greater part of any story is generally not so much what happens as how it's told and why.
Although evolutionary theory had been rattling around for some time when The War of the Worlds was written, Darwin's On the Origin of Species appeared only forty years earlier, so it seems safe to assume that both English society and the scientific community may still have been grappling with the wider meaning of its universe having been recently reconfigured with God no longer at centre stage. Not only had humanity become an aspect of nature rather than some divine creation stood to one side, but assumed divine rights such as those which inspired the civilised to conquer the supposedly uncivilised could no longer be taken for granted. So, just in case it isn't bleeding obvious, The War of the Worlds doubles up as mankind colonised by an imperial force more powerful than itself - casting the Englishman in the role of all those natives of distant, less technologically developed lands; and by letting us know how it feels to find oneself just that little bit further down the food chain:
Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us.
Furthermore, The War of the Worlds does all of this without fuss or sloganeering, focussing on the small scale of its narrator struggling to survive in occupied Kent in a way that recalls, of all things, the best of Robinson Crusoe. My only criticism would be in respect to Isaac Asimov's afterword which seems to miss a point in assuming the story is about the possibility of life on Mars, although that's hardly Herbert's fault. Generally speaking, this one of those rare near-perfect novels which gives you pause to wonder why anyone bothered to write science-fiction ever again.