Disney has sued itself a few times also. While I don't know about Stan Lee's case, at least some of the Disney cases involved one unit or company using intellectual property (IP, trademarks in those cases) owned by another unit without permission. It might not seem like a big deal, since the parent company owns all of it anyway; but part of IP law is that to claim ownership of IP the owner must defend it against infringement else the IP may become public domain or the new user could even assert ownership. So one part of Disney (the IP owner) had to file suit against another part (the one who infringed on the trademark) in order to be able to assert ownership in possible later cases. They might not be asking for any money, and it won't go to court, but it puts the IP owner on record as defending their property. From what I understand, it's a fairly common occurrence in large media conglomerates.