This is the 15225th most frequent Russian word.
популярного
"Popular."
The word 'популярного' is used here as an adjective in the genitive singular masculine form, modifying 'автора', indicating possession or association.
Я купил книгу популярного автора.
I bought a book by a popular author.
Here, 'популярного' again acts as an adjective in the genitive singular masculine form, describing 'певца', suggesting the singer's widespread acclaim.
Мы посетили концерт популярного певца.
We attended the concert of a popular singer.
In this sentence, 'популярного' is an adjective in the genitive singular masculine form, characterizing 'режиссёра' to denote the director's popularity.