Warren Buffett sits in his Omaha office partway through HBO’s new documentary on his life, thumbing through a decades-old manual of corporate reports.

“Is this like going through an old family album?” an off-camera interviewer asks him.

“Better,” Mr. Buffett says, smiling.

“Becoming Warren Buffett,” which airs Jan. 30, recounts the oft-told story of the legendary investor and philanthropist, mostly in his own words. The movie focuses on Mr. Buffett’s family relationships, particularly with his first wife and his father, and the personal sacrifices he made while building his business empire.

Close Buffett watchers will find little to learn. Biographies and articles have retold Mr. Buffett’s life story in detail. And the film doesn’t devote much time to Mr. Buffett’s investment decisions as chairman and chief executive of Berkshire Hathaway Inc., one of the largest companies in the U.S.