He wears a full set of Stormcloak officer armor or Imperial light armor and carries a leveled One-Handed Weapon like a Steel War Axe, based on the faction with which the Dragonborn is aligned. If not aligned with any faction, Captain Valmir's armor will vary depending on who the Dragonborn was with when entering the keep at Helgen.
When spoken to, Captain Valmir gives the Siege on the Dragon Cult quest, where he requests the retrieval of a Dragon Priest Mask known as Rahgot from Forelhost. Also, as an optional task he asks for Skorm Snow-Strider's Journal.
After finding the Dragon Cult Mask and exiting Forelhost, Captain Valmir will be seen dressed as member of the Imperial Legion or a Stormcloak Commander talking to an Imperial soldier or Stormcloak soldier (the opposite of whichever faction he is for the Dragonborn). Captain Valmir is trying to coax the soldier to enter Forelhost to retrieve the mask. After spotting the Dragonborn, the Captain stutters his words then attacks the Dragonborn and the soldier.
Captain Valmir's corpse has a piece of paper with Valmir's Orders. He was an impostor pretending to be an officer of either the Legion or the Stormcloaks to fool soldiers into going into Forelhost to get the Dragon Priest Mask for him.
By looking at the orders and scrawled notes left on the corpse of a bandit or mercenary in Labyrinthian's Dragon Mask area, it appears that Valmir was a Thalmor Soldier or a mercenary of Thalmor descent associated with a Mage or sorcerer who was attempting to unlock the Masks' secrets or to acquire the final mask in the collection. Since the Sorcerer in question and his entourage were all dead upon discovery, it is unlikely Valmir was aware his employer and allies had been slain, and was continuing his mission as normal.
- The General has sent me to obtain a powerful weapon for the war effort.
- This was the last great bastion of the Dragon Cult, and their leaders mask was reported to be quite powerful
- It seems that after the strength of the Cult was broken in the Dragon War a last contingent came here to create a stronghold and regroup.
- Sometime after the quest is finished, thugs may show up and attack the Dragonborn. Their orders will be from the captain.
- Captain Valmir will say: "Return to me once you've obtained the staff." even though the objective is to obtain Rahgot's mask.
- Although he is a captain, he wears the same armor as any Imperial soldier, instead of the heavy Imperial armor which is traditional for a captain to wear. But he does wear the Stormcloak officer armor, instead of normal Stormcloak armor.
- Even when he is wearing Stormcloak officer armor, he says " The General has sent me to obtain a powerful artifact." This lets the Dragonborn know he hasn't quite gotten his story straight and is making it up as he goes.
- When he is speaking with the soldier after the mask is retrieved, his armor may be of the opposite faction if the Dragonborn had worked further with said faction after the quest was started.