Not much new to add to the above recommendations.
Narcos, lot's of subtitles though, so if that's an issue for him, and he doesn;t soeak spanish, may want to pass
Peaky Blinders is good
Bloodline is solid. It's slow, but good.
Band of Brothers is a GREAT series (I believe it is on Netflix, definitely on HBO GO)
Oz
...and I'm probably the latest to the party, just started House of Cards, so far so good thru most of season 1
If you have Amazon Prime... The Wire is a must