Q: Who is the first author of any scientific literature?
Please refer to the ICMJE’s guidelines on authorship criteria.
The first author is the one who conceptualizes the study design, contributes significantly to the progress of the research work and takes it to a logical completion (as per the research proposal), acquisition & analysis of data, who drafts the manuscript and who is responsible for the authenticity of the entire study and the contents presented in the manuscript.
Sometimes, there can be two first authors if each of them has contributed substantially towards the study. The first author can also be the corresponding author, but not always. The supervisor can also be the co-first author depending upon how much he/she has contributed to the work.
Many universities mandate that the research scholar needs to have first author publications for graduation; hence, the research scholar who has done the actual bench/field work along with the above-mentioned aspects is the first author with or without the supervisor being the co-first author.