Horatio Nelson

Lord Admiral Horatio Nelson (died 21st October 1805) was a British admiral who fought in the Napoleonic Wars. He defeated Napoléon Bonaparte's fleet at the Battle of Trafalgar, though it cost him his life. (DWA: H.M.S. TARDIS, PDA: World Game)

Encounters with the Doctor
He twice met the second incarnation of the Doctor, once as he was about to be killed on the HMS Victory, and once shortly before that.

From the Doctor's point of view, their first meeting was when he, Ben and Polly materialised on the Victory. Ben, a fellow sailor, was very eager to meet Nelson, and convinced Nelson that he should send the famous battlecry, "England expects that every man this day will do his duty," to the rest of his fleet. The Doctor, for his part, attempted to change history and prevent Nelson from being killed, but he was unsuccessful. During the whole of the encounter, Nelson seemed more amcable to the TARDIS crew than did his flag captain, Thomas Hardy. (DWA: H.M.S. TARDIS)

Much later in the life of the second incarnation of the Doctor, he was sent by the Celestial Intervention Agency with the Time Lady Serena to investigate unauthorised time meddling during the Napoleonic Wars. He discovered that a Player called the Countess intended to kill both Nelson and the Duke of Wellington simultaneously, thereby completely re-writing world history. In the course of his investigations into the Countess' activities, he had occasion to meet Nelson again. PDA: World Game)

Doctoral name dropping
Later versions of the Doctor were likely, but not necessarily, trading on these two encounters with Nelson when they dropped the admiral's name. While talking to a Royal Navy officer the Third Doctor claimed that Nelson was "a close personal friend". (DW: The Sea Devils) The Fourth Doctor claimed that he had breakfast with Nelson the day before the Battle at Trafalgar. (PDA: Eye of Heaven) In his eighth incarnation the Doctor claimed to have been "instrumental" at Trafalgar. (EDA: The Scarlet Empress)