A biography is a story of a person's life, written by another author. The writer of a biography is called a biographer while the person written about is known as the subject or biographee.
Biographies usually take the form of a narrative, proceeding chronologically through the stages of a person's life. American author Cynthia Ozick notes in her essay "Justice (Again) to Edith Wharton" that a good biography is like a novel, wherein it believes in the idea of a life as "a triumphal or tragic story with a shape, a story that begins at birth, moves on to a middle part, and ends with the death of the protagonist."
A biographical essay is a comparatively short work of nonfiction about certain aspects of a person's life. By necessity, this sort of essay is much more selective than a full-length biography, usually focusing only on key experiences and events in the subject's life.
Between History and Fiction
Perhaps because of this novel-like form, biographies fit squarely between written history and fiction, wherein the author often uses personal flairs and must invent details "filling in the gaps" of the story of a person's life that can't be gleaned from first-hand or available documentation like home movies, photographs, and written accounts.
Some critics of the form argue it does a disservice to both history and fiction, going so far as to call them "unwanted offspring, which has brought a great embarrassment to them both," as Michael Holroyd puts it in his book "Works on Paper: The Craft of Biography and Autobiography." Nabokov even called biographers "psycho-plagiarists," meaning that they steal the psychology of a person and transcribe it to the written form.
Biographies are distinct from creative non-fiction such as memoir in that biographies are specifically about one person's full life story -- from birth to death -- while creative non-fiction is allowed to focus on a variety of subjects, or in the case of memoirs certain aspects of an individual's life.
Writing a Biography
For writers who want to pen another person's life story, there are a few ways to spot potential weaknesses, starting with making sure proper and ample research has been conducted -- pulling resources such as newspaper clippings, other academic publications, and recovered documents and found footage.
First and foremost, it is the duty of biographers to avoid misrepresenting the subject as well as acknowledging the research sources they used. Writers should, therefore, avoid presenting a personal bias for or against the subject as being objective is key to conveying the person's life story in full detail.
Perhaps because of this, John F. Parker observes in his essay "Writing: Process to Product" that some people find writing a biographical essay "easier than writing an autobiographical essay. Often it takes less effort to write about others than to reveal ourselves." In other words, in order to tell the full story, even the bad decisions and scandals have to make the page in order to truly be authentic.