There are several accounts that state for around a year Einar roamed Skyrim as a wolf, hunting and obeying Hircines will. Whatever occured between his parents deaths and his enlistment into the Imperial Legion is irrelevant. Einar joined the Legion to battle the Thalmor and keep them out of Skyrim, no damn elf is going to keep him from enjoying the hunt. He didn't quite agree with the Legions ideals but better them than the elves of the Aldmeri Domnion.
Records catch back up to him in 4E 173 in Hammerfell. Einar was under the command of General Decianus and had made a name for himself in several battles. His fellow legionnares took to calling him Wolf-Heart due to the ravenous nature of his fighting and the fire in his eyes when he saw the first bit of bloodshed. Some soldiers swore they saw him rip the throats out of Thalmor troops bare handed. His ferocity was how he channeled his urges to transform and each battle made it harder to control.
Four months of battle after battle through countless victories and defeats, Einar eventually found himself in charge of a legion. Einar, unlike the other leaders, chose to fight on the front lines with his soldiers, earning their respect. His battleaxe cut through the Dominions soldiers like knife through butter, each kill only fueling his hunger for more blood. Thalmor casualty reports suggest that in a span of one night an entire camp of soldiers were ripped apart and mawed by a massive wolf indicating Einar lost his control and went on a frenzy.
Einars legion became so accredited that Titus II ordered them back to northern Cyrodil for a push back into the Imperial City to reclaim it from the Dominion. Einar was put under General Jonna's command with other Nord soldiers near Cheydinhal. History speaks for itself from here, The Battle of Red Ring, and Einar forged his name in the Legion at the capital. Aldmeri soldiers filled the streets and Einars soldiers began tearing their way through them advancing toward the White Gold Tower. Worn and weary from battle, Einars men suffered heavy losses before making into the market district. Night had fallen and Nirns moons would soon be up. Einar turned a corner to move up the street to the next set of buildings. As his eyes scanned the open area, a Bosmer on a roof shot an arrow striking Einar in the chest.
Darkness called for him, Einar could feel himself slipping from this world, he could see Sovngarde, could smell the mead, hear the revelry of the chamions before his time but all this was quickly ripped away when a familiar voice called for him.
"This is not your time, hound. No hall of valor waits for you after your death, just The Hunt. As my most honed tool, I am not done with you. Feed on these mortals flesh. Go my Alpha, sate your hunger."
Einar rose back up as the wolf. He reveled in the surprise on the Elves faces and the shock on the Legions. Arrow after arrow tried to pierce his flesh but his hide was too thick. Einar jumped over barricades and ripped through the tender flesh of the Mer. His poweful arms sending soldiers flying into rubble, breaking their bones. The Legion soldiers looked on with severe shock, records say that the soldiers were envious of his power, but I would say they feared him.
Einars mighty claws ripped straight through the chest of an Altmer battlemage and he pulled the heart of the elf out and after turning to the rest of the Aldmeri soldiers, devoured it whole. The soldiers were demoralized to a point that they fled from the city scholars would later write.
Dawn broke, and Einar relished over the mound of corpses he had amassed. A storm was on its way, Einar could see the clouds moving in. He laid on top of the corpses, laughing, he knew Hircine saved him. Oh how he knew the Daedric Prince would take this out of his hide. He didn't get to relish his victory for long before two Imperial Officers stood over him and ordered that he be stockaded.
There are no records of how long he stayed imprisoned, just that he was released and branded a monster, kicked out of the Legion, stripped of any honor he held with them and shipped back to Skyrim after the White Gold Concordat was signed banning Talos worship in the Empire.
Now, beaten down and disheartened, Einar tried to make his way in Skyrim. Most of this time he spent hunting and trying to make a living selling hides. Hircine never called for him and he learned to control his transformations. On one trip into Falkreath, the sight of a young Nord woman in the genral goods store caught his eye. She was slender and beautiful, her auburn hair shining in the dim candlelight of the store. Einar had never seen a woman so gorgeous, her subtle curves calling to his lesser urges. Einar didn't know what to say to her but spent several days making trips to Falkreath just to see her.
On one of his trips to Gray Pine Goods, Solaf, the shopkeeper, noticed he was looking for her.
"She's not here lad, whats your interest in her anyway?" he asked.
"I uh....," Einar stumbled over his words trying to find an answer.
"I see, you are smitten with the young lass. She works on a farm by the lake. Eira is her name. If you want to make a good impression, she likes purple mountain flowers with deathbell. Tell you what, I'll give you some deathbell and tell you where to pick some of the purest colored mountain flowers. Just do me a favor and don't ever hurt my neice." Solaf handed Einar some of the flowers and a small map that would lead him up towards Helgen to collect the others.
Einar thanked him very much and left the city. He wanted to woo Eira, he felt strongly for her and she would be his. There is nothing that he couldn't conquer and her heart would be his next great victory.
