Margolag is an orc who aided the Horde in the battle of Northwatch Hold. Upon their victory among of the Horde forces became confused when Garrosh Hellscream decided to wait instead of pressing the attack upon Theramore. In response members of the Horde like Baine Bloodhoof, Vol'jin, Frandis Farley, and Kelantir Bloodblade gathered together to discuss what Garrosh was thinking and Margolag was present not only for himself but as a representative for Eitrigg. Unknown to everyone present treachery from within had tipped their meeting off to the Warchief and his bodyguard the Blackrock orc Malkorok. While Margolag was not punished he was ordered to return to his encampment. When Garrosh gave the order for the Horde to move onto Theramore as apart of the army Margolag joined the battle.
Following battle of Theramore it is unknown what happened to Margolag. If he survived the failed siege of the city, he could of been killed in the "accident" in the Razor Hill Inn, along with others like Frandis and Kelantir who voiced disagreement with Warchief Hellscream. Alternatively he may have survived Theramore's fall and merely reported to Eitrigg in Orgrimmar.
As Eitrigg later sends a message to Thrall, the former Warchief of the Horde, the messenger may have been Margolag. After all with Malkorok and the Kor'kron about, it would make sense for Eitrigg to send someone he trusts like Margolag to deliver the message.