The phrase "principal author" refers to the main person responsible for creating or writing something, such as a book, article, or research paper. They are considered the primary or main author of the work. Full definition
In an excellent post just released by The 21st Century Principal the author writes about yet another two companies calculating value - added for school districts, again on the taxpayer's dime. (vamboozled.com)
As principal author of Lonely Planet's World Food series, he'll go anywhere and eat anything for that ultimate foodie high. (burn-blog.com)
More recently Terry completed the project to which she has devoted much of her tenure at the museum, serving as principal author of a two volume scholarly catalogue American Paintings in the Brooklyn Museum: Artists Born by 1876. (nypl.org)