Dan said:
why did they keep calling him Rupin?
There have been several legal problems over Lupin's name over the years, as the character was intended to be the grandson of the original Arsene Lupin, a fictional gentleman theif created by Maurice Leblanc back in the 1900's. However, Monkey Punch created Lupin III without the permission of the Leblanc estate and while the original works were still in copyright. This has led to Lupin occasionally having his name changed due to threat of litigation (
Rupin, Wolf, and somewhat hilariously
Edgar in Leblanc's native France).
Now that the original stories are out of copyright and public domain though, there's no longer any problem with calling him Lupin.