Not sure I'd consider myself big name.
You made Chapter Master.
More accurately, someone else created Chapter Master, the Duke just continued the good work and passed it on.
Someone else created the idea of chapter master. And there was another take on the project which ended up not reaching a playable release. Duke didn't use anyone else's existing codebase for the project, though.
Don't think that's quite accurate. I think he did cobble together some existing scrap code others had worked up to get to the releases he had, before he added a ton of his own work on top of it. Could be wrong though.
Though I can't attest to Duke's practices obviously, I can tell you that the original was made in VB.Net and C++, while Duke's is made entirely of GML. The two(three) langauges are obviously similar and probably share some syntax, but he categorically could not have just copied over some existing work from one to the other..
While I might not choose to continue his work from the GML code due to limitations in the language/engine and the difficultiesi n cleaning the code of someone who's learning as they go, that isn't at all to diminish the fact that he clearly put in a hell of a lot of work to Chapter Master and should be recognised for that.
To say that he just picked it up and then passed it off would be an ill-informed insult to his work, whether you like Chapter Master or not.