That's funny. I actually used to bowl with a Vietnamese guy who's middle name was The. It was pronounced "tay", but in writing it looked like his name was Lee the Do.
Really really messed up mind, but it took me a while to get Gandalf. - No, not called "Christian the Grey" and no, it's not "Dorian the Grey" either. Damn. I *should* .. oh yeaaaah!
Could "Hank" be acceptable as an alternative answer for "the Knife"? There was a quite popular rock band in the Netherlands in the 1970s called "Hank the Knife and the Jets" - https://nl.wikipedia.org/wiki/Hank_the_Knife_%26_the_Jets
How about Eugene the Jeep (old Popeye character), Harriet the Spy (novel/movie character), Barney the Dinosaur (Children TV character) or Shaun the Sheep (British children TV/movie character)?
The Song 'Mack the Knife' was released in 1959, that is 58 years ago!..... how many songs of today will still be remembered by 50% of the quizzers in 2092?
Definitely know Æthelred, not the others though. I do know will o'the wisp as a very old folkore entity. But not as a kids tv thing. (though almost everything from folklore has ended up being us in modern things (usually with 90% of its features stripped and definitely the backstory scrapped) like videogames and cartoons.
You just can't use "the Great" as a history clue. There are just too many. Alexander, Cyrrus, Catherine, Peter, just to name a few. Of course, if you want comment section full of "you should accept xy as a type in" ... :-D
I'm pretty sure he is way more well know and Charles Martel, even in english. And despite it meaning the same, I just can't se "the Hammer" as a clue that can be reasonably expected to get more than a couple of percent.
Never heard of bruce moocher merciless and the greek. Oscar is not know here with the grouch part (and is a very very rare character, not sure if he appears more in the us version of sesame street
Ronal the barbarian is a movie too and it is AWESOME you really should see it (and would be cool if it was added as an acceptable answer aswell, though conan is obviously fine as the main answer, got a bit more history)
I originally tried Maximus the Confessor. The title of confessor has been given to numerous individuals in the Roman Catholic and Eastern Orthodox traditions. I believe it has usually been given to those who suffered for their faith but were not martyred.
Sometimes it's good that your answer doesn't work, because that stretches your knowledge :)
Popeye the Sailor man, Skippy the bush kangaroo, Larry the Cucumber :)
Kermit the Frog
Jabba the Hutt
Winnie the Pooh
Sonic the Hedgehog
Yes I'm sure they are all "People"
Thomas the Tank Engine should be in "books", shurely?