Solid Snake- I wanted someone who was good in action, adventure and violent movies so I got Gerard Butler. To me their is a slight resemblance but i'm not sure with you.
Meryl Silverburgh- Since she is a red-head the first thing that came into my mind was G.I. Joe's Rachel Nichol.
Gray Fox- Since this guy was a ninja I wanted someone who is an actor and stuntman/martial artist so I got Ray Park who is obvously famous for Darth Maul and Snake Eyes.
Hal "Otacon" Emmerich- When I first saw his face I thought to my self I've seen him before but as I was thinking it wasn't him that I saw before but it was Cillian Murphy.