Does Kleiner know about G-man's existence? I know this question is probably asked a lot but its also one I think about a lot and its an interesting question, theres a lot of things for and against both sides. 1. Eli, Its heavily implied Eli and Kleiner escaped Black-Mesa together, and we know that G-man had interacted with Eli on several from telling Eli to prepare for unforseen consequences or supposedly saving Alyx for his own reasons, if Eli and Kleiner had escaped Black-Mesa together it would make since Kleiner would have seen G-man with Eli. 2. The HEV suit, during G-man's speech at the end of Half-Life 1 he says that Gordon has earned to keep his HEV Suit, However, at the start of Half-Life 2 Gordon lacks his suit, but when we reach Kleiner's Lab he hands us the HEV mark 5, he states he modified Gordon's suit, its possible G-man gave Kleiner Gordon's suit to modify so Gordon would be more prepared for the events of Half-Life 2, we know G-man isnt picky with who we talks to get what we needs, we see him talking to oddesa a random general who his fellow rebels don't even take seriously. However, there are some holes in those theories. 1. G-man's powers, G-man has all sorts of reality bending fuckery, its possibe who could just teleported him and Eli away from Kleiner or one else who could have been there, we don't know the full extent of G-man's powers but it's very much possible who could just teleport someone away. 2. Its a different suit, its very much possible its a different HEV suit then the one in Half-Life 1, its possible that Kleiner modifying the suit could just mean he improved the pre existing design, The mark 5 also visually looks less sophisticated then the mark 4, this would make since if it was make from scratch as the rebels would have far less access in material to make the suit then Black Mesa did. I'm interested on what other people thing about this.
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These are good questions. I think Isaac knows because Eli is a good friend of his, and I am certain he would confide in Isaac that he had several interactions with a time-bending, reality defying entity, it's possible he has never see Gman, but I imagine he was at least told of Gman. We don't know where the HEV Mk V comes from, but I'm inclined to believe it is a Mk IV, given to them by the Gman, which Izzy then modified, I figure that they wouldn't normally have access to HEVs, the nature of their equipment is very cobbled together and improvised, I imagine the Combine would take notice of someone smuggling in or stealing an HEV suit, if there were any outside of the BMRF. There's also some clues in the dialogue, the way Isaac talks about it makes it seem like it's the old suit, although he coud be talking figuratively.
You never see Kleiner and Gman in the same time. Also, Kleiner have suit from HL1 that Gman is promise to not take. Maybe he is a Gman ???