[eureka]

Hope this will help.

Here is a Python 3 script for printing author name basing on your commit message format:

Spoiler:

#!/usr/bin/env python3

import fileinput
from itertools import chain
import re

# Author names are delimited with comma and spaces after it.
AUTHOR = re.compile('(?:,\s*)?(?P<author>[^,]+)')

def get_authors(commit_log_line):
    leading_spaces, note, authors = commit_log_line.rpartition(' Authors: ')
    # Check for split being done and if prefix really consisting of spaces
    # only (prefix check is a sanity/paranoid check).
    if authors != commit_log_line and not leading_spaces.strip():
        return AUTHOR.findall(authors.strip())

# `chain.from_iterable` flattens list of lists, then `set` removes duplicates.
authors = list(set(chain.from_iterable(
    # Transform stdin line into list of authors or None (if authors were not
    # found in that line) and then filter out None's.
    filter(None, map(get_authors, fileinput.input()))
)))

if len(authors) == 0:
    print("Kevin Hendricks")
elif len(authors) == 1:
    author = authors[0]
    if author == "KevinH":
        print("Kevin Hendricks")
    else:
        print(author)
else:
    print('Various authors')

It could be tested with:

$ git log -n1 <commit_id> | python3 authors.py

For example:

$ git log -n1 af0740a3 | python3 authors.py
Kevin Hendricks
$ git log -n1 80150331 | python3 authors.py
Kevin Hendricks
$ git log -n1 7b32b687 | python3 authors.py
tkeo
$ git log -n1 91d3e282 | python3 authors.py
Various authors

And this script could be used with the following --env-filter parameter for git filter-branch:

--env-filter 'export GIT_AUTHOR_NAME="$(git log -n1 ${GIT_COMMIT} | python3 /full/path/to/authors.py)"; if [ "x${GIT_AUTHOR_NAME}" != "xKevin Hendricks" ]; then export GIT_AUTHOR_EMAIL=""; fi'

This is the result:

Spoiler:

$ git log|grep '^\(Author\|Date\):'

Author: Kevin Hendricks <kevinhendricks@users.noreply.github.com>
Date:   Tue Oct 14 18:21:13 2014 -0400
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Fri Oct 10 00:00:00 2014 +0000
Author: Various authors <>
Date:   Sat Sep 13 00:00:00 2014 +0000
Author: Various authors <>
Date:   Tue Jul 15 00:00:00 2014 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Thu Jul 10 00:00:00 2014 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Thu Jul 10 00:00:00 2014 +0000
Author: Various authors <>
Date:   Thu Jul 10 00:00:00 2014 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Thu Jul 10 00:00:00 2014 +0000
Author: Various authors <>
Date:   Tue Jul 8 00:00:00 2014 +0000
Author: Various authors <>
Date:   Thu Jun 26 00:00:00 2014 +0000
Author: Various authors <>
Date:   Wed Jun 25 00:00:00 2014 +0000
Author: tkeo <>
Date:   Sun Jun 22 00:00:00 2014 +0000
Author: Various authors <>
Date:   Wed Jun 18 00:00:00 2014 +0000
Author: Various authors <>
Date:   Tue Jun 17 00:00:00 2014 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Sat Jun 14 00:00:00 2014 +0000
Author: Various authors <>
Date:   Tue Jun 10 00:00:00 2014 +0000
Author: Various authors <>
Date:   Sun May 18 00:00:00 2014 +0000
Author: Various authors <>
Date:   Sat Apr 26 00:00:00 2014 +0000
Author: Various authors <>
Date:   Sun Feb 23 00:00:00 2014 +0000
Author: tkeo <>
Date:   Sun Feb 16 00:00:00 2014 +0000
Author: tkeo <>
Date:   Sun Feb 9 00:00:00 2014 +0000
Author: Various authors <>
Date:   Mon Apr 22 00:00:00 2013 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Fri Jan 17 00:00:00 2003 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Fri Jan 17 00:00:00 2003 +0000
Author: Various authors <>
Date:   Mon Dec 10 00:00:00 2012 +0000
Author: Various authors <>
Date:   Sat Oct 27 00:00:00 2012 +0000
Author: Various authors <>
Date:   Fri Oct 26 00:00:00 2012 +0000
Author: DiapDealer <>
Date:   Thu Sep 13 00:00:00 2012 +0000
Author: Various authors <>
Date:   Wed Jul 25 00:00:00 2012 +0000
Author: Various authors <>
Date:   Thu Apr 26 00:00:00 2012 +0000
Author: Various authors <>
Date:   Fri Mar 23 00:00:00 2012 +0000
Author: Various authors <>
Date:   Thu Mar 8 00:00:00 2012 +0000
Author: Various authors <>
Date:   Sun Feb 12 00:00:00 2012 +0000
Author: Various authors <>
Date:   Fri Jan 27 00:00:00 2012 +0000
Author: nickredding <>
Date:   Fri Jan 27 00:00:00 2012 +0000
Author: Various authors <>
Date:   Wed Jan 18 00:00:00 2012 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Fri Dec 23 00:00:00 2011 +0000
Author: Various authors <>
Date:   Thu Oct 27 00:00:00 2011 +0000
Author: pdurrant <>
Date:   Thu Sep 1 00:00:00 2011 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Fri Aug 5 00:00:00 2011 +0000
Author: siebert <>
Date:   Sat Jul 23 00:00:00 2011 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Tue Jul 19 00:00:00 2011 +0000
Author: siebert <>
Date:   Mon Jul 18 00:00:00 2011 +0000
Author: Various authors <>
Date:   Mon Jun 27 00:00:00 2011 +0000
Author: pdurrant <>
Date:   Wed May 18 00:00:00 2011 +0000
Author: pdurrant <>
Date:   Sun Aug 29 00:00:00 2010 +0000
Author: pdurrant <>
Date:   Mon Apr 12 00:00:00 2010 +0000
Author: pdurrant <>
Date:   Sat Mar 13 00:00:00 2010 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Thu Feb 18 00:00:00 2010 +0000
Author: pdurrant <>
Date:   Thu Feb 18 00:00:00 2010 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Thu Feb 18 00:00:00 2010 +0000
Author: pdurrant <>
Date:   Wed Feb 17 00:00:00 2010 +0000
Author: pdurrant <>
Date:   Thu Feb 11 00:00:00 2010 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Mon Feb 8 00:00:00 2010 +0000
Author: Various authors <>
Date:   Sun Feb 7 00:00:00 2010 +0000
Author: pdurrant <>
Date:   Fri Feb 5 00:00:00 2010 +0000
Author: Kevin Hendricks <kevin.b.hendricks@noreply-github.com>
Date:   Thu Nov 12 00:00:00 2009 +0000

I guess, author of the very first commit should be fixed manually.

I think, Git allows only for one author in commit field, so historical information about authors shouldn't be removed from commit messages.