I love Liquid Snake, he's such a badass. He's a stereotype in every sense of bad guy, from his looks to his sound, but goddamn he's awesome.
I think Liquid owns a lot to Karl from Die Hard. Kojima is a big fan of American action movies so he probably just made a caricature/homage to Karl, the ultimate European terrorist. Kinda like how Solid Snake is a homage to Snake Plissken.