Posterity will ne’er survey
a Nobler grave than this:
Here lie the bones of Castlereagh:
Stop, traveller, and p*** !

Robert Stewart, Viscount Castlereagh (which rhymes with “pray”, if you choose to have that, rather than “piss”, as the last word of Byron’s little poem) was an Anglo-Irish politician who managed to make himself throughly hated.

Though generally in favour of concessions to the Irish he did not support Catholic Emancipation from the discrimination and civil disabilities they suffered under as disenfranchised second-class citizens. He took the lead in suppressing the Irish Rebellion of 1798; he advocated leniency to the common people but had leaders executed – including a Presbyterian minister who had canvassed for him in an election. From 1812 to 1822 he was the British Foreign Secretary, instrumental in managing the alliance that defeated Napoleon; and then at the Congress of Vienna, with the conservative Bourbons back on the throne of France, he advocated leniency for France and non-intervention by the UK in European affairs – which was seen as siding with the repressive Eastern European powers. This is from the ‘Dedication’ to Byron’s ‘Don Juan’:

Cold-blooded, smooth-faced, placid miscreant
Dabbling its sleek young hands in Erin’s gore,
And thus for wider carnage taught to pant,
Transferred to gorge upon a sister shore
The vulgarest tool that Tyranny could want,
With just enough of talent, and no more,
To lengthen fetters by another fixed,
And offer poison long already mixed.

Castlereagh’s suicide in 1822 further occasioned this from Byron:

Oh, Castlereagh! thou art a patriot now;
Cato died for his country, so didst thou:
He perish’d rather than see Rome en­slaved,
Thou cutt’ st thy throat that Britain may be saved!
So Castlereagh has cut his throat!–The worst
Of this is, – that his own was not the first.
So He has cut his throat at last!–He! Who?
The man who cut his country’s long ago.