I would like to suggest Robert Service's excellent biography of Stalin

I would suggest three books. Or rather, depending on what you would like.

Stephen Kotkin is writing an amazing comprehensive series on Stalin that covers it all, from his birth to his death. The first part of the series is done and covers up to and through the Revolution and his rise of power in the 1920s. It is called "Stalin Volume I: Paradoxes of Power 1878-1928"

The other ones are both by the same author, Simon Sebag Montifiore one of them being "Stalin: In the Court of the Red Tsar" which deals with Stalin in power. And the other is "Young Stalin" which deals with Stalin before rising to power.

I hope this helps.