Why do we use the definite article in "the other"?

Why in the sentence "One suspect was a male youth, while the other was an adult man." we use 'the' before 'other'. I have to explain its function.


Solution 1:

In English the is the most frequently used definite article.

We use the definite article in front of a noun when we believe the listener/reader knows exactly what we are referring to.

Link: The definite article: 'the'

So, here in the sentence

One suspect was a male youth, while the other was an adult man.

we use the because it is being referred to a definite other