The Stormcloaks

 are the standing army of the Imperial Province of Skyrim. They started out as a militia led by Ulfric Stormcloak to free the Reach from the Reachmen that had taken it from the Nords in 4E 175. In 4E 201 the faction later became a rebel army led by Ulfric, who by the time became Jarl of Eastmarch, whom fought against the 4th Imperial Legion in a Civil War. After they won the war in 4E 203 and Ulfric became the High King of the Province they became the official standing army.

Ranks
The Stormcloaks don't use orthodox military ranks, they instead use titles. This is something they carried over from their militia roots.
 * Stormblade
 * Bear-Heart
 * Winter-Axe
 * Snow-Hammer
 * Bone-Breaker
 * Blue-Blood
 * Ice-Veins
 * Unblooded

Other titles:
 * Battle-Maiden: A Nordic term used for female military healers