Saw Stallone post about this and he said that Dennehey was instrumental in how he shaped Rambo as a character thanks to his input about his own personal Vietnam experience.
I saw him once, back in 1993, in a pub on the Norfolk Broads. He greeted everyone as he came in, ordered a Scotch from the barman, only to be told "sorry sir, it's ten past three!" . I think he found it hard to believe that he couldn't get a drink in a pub in a tourist area in the middle of the afternoon. When he left we told the barman that he'd just turned away a Hollywood actor, but he didn't have a clue who he was.
One of the few actors who are not big names that I'd readily recognise. Solid, reliable performer in a wide range of roles, whose parts I usually enjoyed.