The phrase "first biography" refers to a book or piece of writing that tells the story of a person's life. It means that it is the earliest or very first account of someone's life that has been recorded or written down. Full definition
I have just finished the The Snowball, the first biography Warren Buffett has cooperated with. (monevator.com)
The first biography about Lewis, also titled C. S. Lewis: A Biography, was. (religion-online.org)
In Fierce Convictions, the first biography of More since 2004, Liberty University's Karen Swallow Prior sets out to restore More's reputation. (firstthings.com)