The Sergeant is an unnamed man fighting in the Ogre War in "Manhattan".
Before the Curse
The sergeant warns Rumple about their prisoner. ("Manhattan")
Various soldiers are seen working and resting as we see Rumplestiltskin following a group of men. The sergeant emerges from a tent and addresses Rumple, causing him to stop. The sergeant approaches him and tells Rumple that he's needed at the front, telling him to guard the nearby crate with his life, in the sergeant's stead. Looking at the crate and seeing that the contents is concealed by a covering, Rumple asks what's beneath it, and the sergeant tells him that it's a prisoner who can help them turn the tide against the ogres. He tells Rumple to be careful as it's a tricky beast, before leaving for the front line. Rumple walks over to the wagon containing the covered prisoner and he soon has his future predicted to him by the Seer inside.
Rumple fears the Seer's prediction will come true. ("Manhattan")
The sergeant approaches Rumple and other soldiers and announces that fortune is in their favour. He states that today they shall not be marching into battle, but riding. Rumple asks just what exactly they'll be riding, and the leader wonders what kind of question that is, saying that they'll ride horses "of course". He proceeds to tell the soldiers to grab themselves a cow and get ready. Rumple stops him, asking him to repeat himself, and the leader tells him that they need to grab a cow, which refers to the saddles they got in made from the finest leather. He tells Rumple to grab his so at least the ride into doom will be soft on his backside. ("Manhattan")