This is kind of a hard one to explain. But is there a general consensus on where a historical fades from historical to a sort of "relevent" figure?

An example of this would be the way we might talk about a leader in history. For example I find Atilla the Hun really interesting and in casual conversation I might say I really like him or that he's one of my favourite historical figures. In reality he was one of the most ruthless and evil men probably ever. In contrast to this I could also find the rise of nazi Germany interesting but would never in my right mind say talk about him as a "favourite" of mine.

This kind of carries across into the current debates on statues of historical figures. There are plenty of more ancient figures that no one would ever take issue with having a statue in public, but there is debate on some slightly newer statues that were historically significant but had pretty strong ties to the slave trade or similar negative things.

Edit: I want to add retrospectively that the second question might might not be answerable from a historical perspective for the current climate surrounding the ethics of statues so if there is no interesting history of ethical opinion on statues over 20 years ago please ignore it.