first author
Used in academic publishing to refer to the author listed first on a paper, often the primary contributor.
The first author of this paper is Professor Tanaka.
As the first author, I have the responsibility to compile the research.
共著者 means 'co-author', referring to any author other than the first, while 筆頭著者 specifically denotes the first-named author.
責任著者 is the 'corresponding author' who handles communication, not necessarily the first author, though sometimes the same person.
Compound of 筆頭 (ひっとう, 'head of a list') and 著者 (ちょしゃ, 'author'). The term is a modern academic coinage.