What is the significance of 'The Dark Knight Returns' in the history of Batman vs. Superman comics?

'The Dark Knight Returns' by Frank Miller (1986) is hugely significant. It reimagined Batman as a grim, older vigilante and depicted a confrontation with a government-controlled Superman. This story heavily influenced subsequent depictions of both characters and established a template for darker, more complex Batman vs. Superman narratives, paving the way for events like 'The Dark Knight Strikes Again' and inspiring the DCEU film.