Programs which have many contributors usually include a file named AUTHORS in their distribution, which lists the individual contributions. Emacs has a special command for maintaining the AUTHORS file that is part of the Emacs distribution.
The M-x authors command prompts for the name of the root of the Emacs source directory. It then scans ChageLog files and Lisp source files under that directory for information about authors of individual packages and people who made changes in source files, and puts the information it gleans into a buffer named *Authors*. You can then edit the contents of that buffer and merge it with the exisiting AUTHORS file.
Do not assume that this command finds all the contributors; don't assume that a person not listed in the output was not a contributor. If you merged in someone's contribution and did not put his name in the change log, he won't show up in M-x authors either.