The beginning of the story reminds me of The Count of Monte Cristo. The character Favraux reminds me of Villefort. Like Villefort has a kind-hearted daughter Valentine, Favraux also has Jacqueline. The movie starts with Favraux, a banker, receives a threatening note from a mysterious man who called himself "Judex" (a latin word for 'judge'), who demands him to pay back the people he has swindled. Favraux's refusal results in his death by midnight during a masked ball when they are celebrating his daughter's engagement. Actually, he is only drugged by Judex, and then his 'body' is kidnapped from the cemetery. His life is spared after Jacqueline refuses the inheritance. Meanwhile, his mistress, Diana, who after his 'death' is left with nothing, plans to steal valuable papers from his house, with the help of her boyfriend. They feel Jacqueline is an obstacle and plan to get rid of her.
I think I prefer Judex as an merciless avenger. There is no explanation in the movie why he wants to punish Favraux, but I think he wants to revenge his father. My feeling turns to be right when in the DVD bonus, fragments from the original film by Feuillade are shown. The banker was Judex's father's partner who drove him to bankruptcy and committed suicide. Favraux also made odious advances to Judex's mother, who made young Judex and his brother to swear revenge. Judex's costumes, a cape and a broad-brimmed hat, are hardly a disguise. They only make him more handsome :-)