After reading the white paper of Satoshi Nakamoto. The white paper does not mention anything about a limit of money supply. I think I have read somewhere mentioned the name, but unfortunately I cannot remember it. If I look in the main resources available online (Wikipedia, bitcoin.org, ..) they all mention Satoshi Nakamoto as the one who added this feature. If Satoshi was not the one to add this feature, I think it is very important that we know who came up with this, and why the bitcoin dev community at the moment decided to adopt it.
This is the announcement of Bitcoin:
Total circulation will be 21,000,000 coins. It'll be distributed to network nodes when they make blocks, with the amount cut in half every 4 years.
first 4 years: 10,500,000 coins
next 4 years: 5,250,000 coins
next 4 years: 2,625,000 coins
next 4 years: 1,312,500 coins etc...
It was part of it from the beginning, and it definitely wasn't secret.