Who is Major Michael Hogan from Sharpe's Honour: Richard Sharpe and the Vitoria Campaign, February to June, 1813 and what is their importance?

With his reputation in tatters, Michael Hogan meets Sharpe at the Gateway to God, where he requests three things...... that Sharpe instruct him in how best to hunt down his enemies, that Sharpe clear his name, and that Sharpe keep himself free from the French.