Michael Hogan is an Irish Major in the Royal Engineers, who serves as a high-ranking 'exploring officer' for Wellington and serves to introduce Sharpe into the murky world of politics and espionage.
In the TV series, Hogan recruits Sharpe under the smokescreen of recovering the missing banker Rothschild while actually manipulating him into joining Colonel Don Blas Vivar for his morale-heightening assault on Santa Compostella, though in the books Sharpe becomes embroiled in these affairs before even meeting Hogan. (Sharpe's Rifles) In both cases, though, the end result is the same: Hogan is greatly impressed with Sharpe's initiative and recruits him as a regular agent, specifically to make a decent fighting battalion out of the run-down South Essex.
In the novels, when Sharpe meets Hogan he is a junior exploring officer, languishing under the incompetent command of Colonel Christopher, a diplomat who bought his commission and wears the uniform of a far-more respected regiment. Hogan is eventually forced to desert, when their position outside Oporto is overwhelmed by the French, reluctantly leaving Sharpe behind to rescue the Colonel's wife. Through a series of misadventures it is revealed that Christopher is a traitor, and almost as soon as Sharpe has returned to friendly territory he and Hogan are ordered to assassinated him by Lord Pumphrey. Hogan's resourcefulness and knowledge of the roads to and from Portugal allowed him to reach the Spanish-Portuguese border before Marshall Soult's army and allowed Sharpe to slay Christopher as ordered - but ironically due to the nature of Sharpe's field promotion and the small number of Engineers officers needed in the Peninsular, neither man was promoted for the notable action(Sharpe's Havoc)
Hogan operates in secrecy and often behind enemy lines, using a detached and cold logic to find his objectives. He disguises this with a strong amount of bluster and feigning ignorance, deliberately appearing short-witted to fool his rivals and calm his acquaintances. A key example of this is seen in the TV movie of Sharpe's Eagle where he tells William Lawford that Wellington's entire strategy is beyond his understanding, when in actual fact he himself played a key part in its orchestration.
Hogan vanishes from the TV movies after only the second film, due to work commitments from Brian Cox, the actor who portrayed him, but in the novels Hogan is a steadfast and recurring ally of Sharpe's, until his tragic death at the worst killer of the wars: fever.
Hogan is succeeded as Sharpe's liaison with Wellington by Major Nairn