Actor - The Empire Strikes Back (Boba Fett, in Cloud City outside Han Solo's torture chamber)
While Jeremy Bulloch was tired up in previous acting arrangements for a while, John -- a stand-in actor who played Dack, Luke Skywalker's snowspeeder co-pilot -- stepped in for the "he's no good to me dead" sequence with Darth Vader.
About the Production
“The reference to Jeremy Bulloch having drawn from Clint Eastwood is absolutely correct. As fans know, I dep’d for Jeremy for two days on ESB in the scene with David, Billy Dee and John Hollis (Lobot). Boba says the line, ‘He’s no good to me dead.’ The day before, I asked Jeremy the usual — ‘What’s my motivation? How do you want me to play this?’ He said very simply, ‘Play Clint Eastwood.’ So when Darth Vader entered to my right and came around to face me, I very slowly and deliberately moved my head mechanically from my right shoulder to face him squarely. I thought of my move in terms of a radar tracking him, not so much for communicating to him, but rather as man-machine weapon system that coolly and continuously regarded him as a target that Boba was ready to take out in an instant.”
While I had two days in costume, I only recall that one day when they shot film. The other day, Irvin Kershner was setting up a scene between Boba and Lando in the carbon freezing chamber itself. We stood around in full costume on the gantry for the part of the day as the crew tried to make it happen. I remember a long conversation with Billy Dee Williams discussing the impact of grandmothers on our understanding of the meaning of life. Around us, first AD Dave Tomlin and his crew tried to work out the shot with Kersh. Dave Prowse may have been there as well, but I don’t remember Peter, Harrison, or Carrie being present.
Source: Becoming Boba: Coming to Terms with an Alter Ego starwars.com