best-selling
prolific
famous, well-known
published
Her ambition was to become a published author.

anonymous
the anonymous author of this pamphlet

children's
Primarily a children's author, she has also written books for adults.

contributing, joint (esp. BrE)
He is a contributing author to many school textbooks.

sole
lead, senior (esp. AmE)
the lead author of the report

favourite/favorite

read
Stephen King is an author I've never read.

cite, quote

write (sth)
The author was writing in the 17th century.

argue sth, conclude sth, note sth, suggest sth
The study's authors conclude that there is insufficient evidence to justify the policy.

Author is used with these nouns as the object:
article, book, paper