I don't think the 4th Hokage created the Reaper Death Seal. Most people do but not me. Most people get that impression because Hiruzen said "this is the 4th's jutsu!" but I don't believe so because he could've said that just because he used it. If Kakashi says "It's Naruto's Rasengan!", does that mean he created it? No, it just sounds better and confuses some people. Or Madara's Susanoo or anything like that. But what do you think?
and if you have proof I would love to see it 