What does UserA committed with UserB 13 days ago on github mean?

Question

I am interested in knowing which one of the two users made the file changes when github lists both. The git record contains only UserA however.

Answer 1

@venkatKA's answer is accurate and descriptive but I thought I'd add a few details.

git cat-file -p HEAD can be used to print out information about the commit

tree d85ed3c3a055c95445898a5119ea0a532459fdsf
parent 0b6ed951b2c04b4134c91ffa053b4330edfdffc1
author AuthA  1487356245 +0000
committer AutbB  1487356245 +0000

If you want to fix historic committers (for example if you are changing your identity) then you can use:

git filter-branch -f --tree-filter "GIT_COMMITTER_NAME='New Author'; GIT_COMMITTER_EMAIL='New Author'" 

The standard comments about rebases breaking history and why revisionism is a bad idea apply.