I always forget to set up my user info on git on new machines before I check stuff in. It’s pretty easy to fix if there’s nobody else in your repo:

git filter-branch --env-filter "\
  export GIT_AUTHOR_NAME=Dade\ Murphy \
         GIT_AUTHOR_EMAIL=zer0cool@example.com \
         GIT_COMMITTER_NAME=Dade\ Murphy \
         GIT_COMMITTER_EMAIL=zer0cool@example.com "

Source: serverfault