I'm one of the team that was hired to take the Excel app that one overdue-to-retire person had spent 20+ years developing (without documentation, and inserting

I'm one of the team that was hired to take the Excel app that one overdue-to-retire person had spent 20+ years developing (without documentation, and inserting every miscellaneous feature he felt was desirable, regardless of actual need, and which, of course, he wanted all of to be kept) for the entire company's metrics and reporting, and turn it into something that could actually be understood by anyone else, with proper database normalization, API access, etc.