Sir Eammon was an loyal and close associate of Morgarath mentioned in The Tournament at Gorlan. His support of the Baron of Gorlan was apparently well known, as he openly plotted alongside Morgarath to aid the Baron in seizing power and was later even tasked with keeping Duncan prisoner in Castle Wildriver, whilst their man Tiller impersonated the Prince and ruined his name. Due to his title, it can be assumed Eammon was at one point a knight of considerable power.
It is unknown what became of Eammon after Morgarath's retreat into the Mountains of Rain and Night. However, as he was actively involved in Morgarath's coup, he might have been incarcerated for his crimes or might have even rendezvoused with the fleeing baron and his loyal soldiers and staff and escaped into the southern mountains. If he did somehow evade punishment, Eammon was presumably among the 'Fence-Sitters' and, if he was one of the nobles Morgarath visited, he most likely was among those like Peller who received the black lord cordially.