I think that your question and the answers of others revolve around bitcoinCore, which we can say that the first developers were Satoshi and Martti Malmi, and after that the developers contributed to the open source code, which was not on github, but rather
http://sourceforge.net.
Martti Malmi
- Minimize to system tray option
- Setup program for Windows
- Linux version (tested on Ubuntu)
Satoshi Nakamoto
- Multi-processor support for coin generation
- Proxy support for use with TOR
- Fixed some slowdowns in the initial block download
The rest of the developers will join one after another.