Lupin was actually the character of a french author's books writen in the 19th century, he was a master thief and stuff... The books became very popular in Japan post-ww2, and a manga series an anime were released based on those books (which resulted in a huge copyright fight over the years, apparently he's both public domain AND not public domain at the same time). The word Lupin is a synonym for "thief" in Japan, like... kleenex for paper tissue.