Change committer and author of all commits in a repo

fix-author-committer.sh

#!/bin/sh

# Credits: http://stackoverflow.com/a/750191

git filter-branch -f --env-filter "
    GIT_AUTHOR_NAME='__AUTHOR_NAME__'
    GIT_AUTHOR_EMAIL='__AUTHOR_EMAIL_ADDRESS__'
    GIT_COMMITTER_NAME='__COMMITTER_NAME__'
    GIT_COMMITTER_EMAIL='__COMMITTER_EMAIL_ADDRESS__'
  " HEAD

run
git rebase -i <sha1 or ref of starting point>

mark all commits that you want to change with edit (or e )
loop the following two commands until you have processed all the commits:
git commit --amend --reuse-message=HEAD --author="New Author <new@author.email>"
and
git rebase --continue

run
git update-ref -d refs/original/refs/heads/master

afterwards