Are you saying it is bad mathoverflow ethics to wiki someone else's question? (I am not being cynical; I am asking this seriously. I'm new here.)

I would have edited the original question and just reopened it if it had been community wiki, but it wasn't, and the person who asked it did not respond to the calls for it to be made so. I don't understand why you're defending this question when the person who asked it was given every opportunity to fix it.

I am rather baffled by the chain of events surrounding the closing and "reopening" of this question.

First, I feel it was unfairly closed. I think it may have been more honest of the closers to wait until the discussion at meta was finished; especially since at least two very respected participants have shown their interest in this question; why were everyone in such a rush to close it before all opinions were expressed?

Second, it had to be community-wikified as soon as possible. Why didn't anyone wiki it? If it had been community-wiki I could (or anyone else could) edit the question so it'd be more along the lines of Harry's "new version".

Third and most important - Harry, you were so eager to close the original question because it was "subjective and argumentative" but the new question is still subjective and still argumentative and for precisely the same reaons the previous question was*. As I've already stated, when asking "who's the last mathematician to have known all of math?", it's IMPLIED you ask about the mathematical development at the era the mathematician lived in (and if you thought this being implied isn't enough, and that it should be more explicit in the question, you could've edited one or two lines in the original question to make this clear). In fact I see the two questions as more or less equivalent (as evidence of this, Wadim Zudilin, who was probably unaware of the original question, commented on your question right after you posted it: "Aren't you asking about who was the last universal mathematician?"). So why did you open a new question rather than simply edit the original one?

*On second thought, your "new" question is likely to get more "discussions" and subjective opinions (which is as far as I understand what the closers were afraid of) than the original question.

Naively, this will measure pure breadth, rather than depth, of knowledge, and the question probably requires an analysis of both. But the depth of understanding of a given mathematician can be evaluated, for example, by studying the importance of their papers (say as judged by contemporary and later opinions).

Here's a copy of the disclaimer I left on the new post, which explains why I did this:

Disclaimer:

I am asking this question as an improvement to this question, which should be community wiki. This is in line with the actions taken by Andy Putman in a similar case (cf. meta).

One could ask something like "at what point in history did it become impossible for a person to understand most of mathematics?" and get information of roughly the same quality.

That certainly sounds more agreeable.

I feel that if it were revised to reduce the "who was the greatest" tone, I'd be less against it.

Same here.

Regarding the question under consideration, I feel that if it were revised to reduce the "who was the greatest" tone, I'd be less against it. One could ask something like "at what point in history did it become impossible for a person to understand most of mathematics?" and get information of roughly the same quality.

Who is the last mathematician who had an understanding of a large proportion of mathematics (at the time they were alive)?

I don't think the arguments using the "totality of mathematics" apply to this question.

I also voted to reopen. I think this is an interesting question in the history of mathematics, and good answers will likely be informative and stimulating (as are some of those already given).

I don't think that a historian of mathematics could ever answer this question for the following reason:

We can say what areas of mathematics a person did work in, but it's very hard to say what areas of mathematics that person understood. The only answer we could give is a pretty bad lower bound (Euclid, perhaps, could be said to have understood all of the pure mathematics of his time, but mainly because the field of pure mathematics was miniscule compared to today. However, even this is not a definitive answer, since it's very possible that large amounts of the work done were lost to the sands of time, so to speak.) Further, this depends integrally on our definition of what constitutes mathematics (was Aristotelian syllogistic logic actually mathematics?)!

Nearly all soft questions could be said to be subjective and argumentative. Do you usually vote to close most soft questions?

I disagree and could find a number of soft questions that aren't subjective or argumentative (I've made a total of seven soft question posts, none of which could be considered either subjective or argumentative. I'm also very careful about what I call a soft question in the tags, so anything not immediately relevant to actual mathematics is marked as such).

Well, it's subjective because a.) it requires us to judge someone's understanding of a subject from insufficient historical evidence. b.) requires us to determine what fields we would consider mathematics, and c.) leads people to choose mathematicians within their own fields.

By c.) above, and since it is very close to the question "who was the best mathematician ever", it seems likely to start an argument.