A hero who lived in the 13th century

[Tanya Carousel]

Hello. In the Student's Workbook "Laser Intermediate" there is a sentence where you must put an article. In the Key answers, the article is " a".
"Robin Hood is  a legendary English hero who lived in the 13th century".
After the word "hero" there goes the word "who" with the clarification who he was.
So, the question is, why is here used the article "a" instead of "the"?
Thanks in advance!

 

[dojibear]

Using "the", the sentence would say that he was the only one (the only legendary English hero who lived in the 13th century). That might be true, or it might not be true.

Using "a", the sentence says that Robin Hood was a legendary English hero who lived in the 13th century, but doesn't say that there were no others.

So you should use "a", unless you want to do research about 13th century England.

 

[velisarius]

The modifying clause "who lived in the 13th century" doesn't make any difference; it just provides more specific information.

Another way if expressing it: Robin Hood was a legendary English hero. He lived in the 13th century. With the modifying clause, the two sentences are merged into one.