Original gopher by Renée French, re-imagined by Søren Siebuhr and then vectorized in Inkscape.
Converting png output from Inkscape to a square image:
gm convert source.png -thumbnail '1150x1150>' -background transparent -gravity center -extent 1150x1150 new.png
Finally, tidy up with pngquant and pngcrush.
Creative Commons Attribution 3.0