Portal fact, Wheatley had voice actors before Stephen Merchant. Richard Lorde from Valve originally voiced him as a placeholder in early development and Richard Ayoade was the first choice before Stephen Merchant.
Source:
youtube
Richard Lorde's placeholder performance:
youtube
Reference for Richard Ayoade (in a video with Stephen Merchant if you wanted to compare their voices lol):
TA DAAAAAA (this design isn’t final it’s just one I’ve been doodling recently and I think it turned out pretty good! And the comment is from a yt video I watched about someone making a real life Wheatley. Honestly I seriously can’t make up my mind about designs 😭
So those moments wouldn't have been completely scripted, you just give direction and sit back?
Stephen Merchant: There'd be a loose bit of script. But we were always encouraging them to add to it, and keep it real. We learned to do that very early on. At first we used to write Tim and Dawn flirtation dialogue, and it was just excruciating when it was performed. It was actually way better if we just let Martin and Lucy talk like friends.
Martin Freeman: That's the first time I've ever heard Ricky or Steve admit that! They used to dislike it when people said it was an improvised show. It wasn't, but anybody who knows me knows that some of those lines came straight from me. Of course they did. But I certainly wouldn't claim a co-write on it. “Scripted but loose”, is how I always describe it.