An alternative to SEDE is Google Search. To search all Stack Exchange sites for a specific name, enter such thing as the search term:
Daniil inurl:/.com/users site:stackexchange.com OR site:stackoverflow.com OR site:superuser.com OR site:serverfault.com OR site: askubuntu.com OR site:stackapps.com
This will search the SE domains, and only in ...
I must have missed that discussion ... anyway, it's relatively simple to write a SEDE query for this. Here is the list of all 145 Daniils in the network. I heard the top one posts a lot of ... eh ... about spam.
(Note that SEDE is updated once a week, on Sunday morning. Brand new spam accounts may not be in there.)
In case you need to search for someone who has helped you before, you can use your inbox or your activity page. You will find any comment or answer coming from that user.
The "Responses" tab on the "Activity" page is very useful. There are several options to list comments, answers or all. As an example, you can find me there from now on.
Stack Exchange is an international network, with users from all countries across the world. If a user's real name is Влади́мир Влади́мирович Пу́тин or 习近平, I can imagine they want to use that and not some transliteration into Vladimir Vladimirovich Putin resp. Xi Jinping. If you'd join a Russian website, you wouldn't want to be forced to choose your name as ...
This was intended (it has actually been there for five years, displaying for any user whose display name changed recently). However, the feature itself is no longer necessary, and has been removed.
For moderators: if a user has changed their display name recently, you will still be able to see this and their recent names in the Account Info dropdown on ...