Cassius was born in 77 AD, in the Flavian Dynasty of the Roman Empire, a foundling taken in as a baby by a Roman soldier and his Gaelic wife in Scotland. The couple raised Cassius as their own. His adoptive father died in battle overseas when Cass was still a boy, and his adoptive mother relied heavily on her family in a small seaside fishing village for support.

At 15, Cassius, mother remarried, but his stepfather was a hard man who had no interest in raising another man's child, let alone the adopted son of another. So Cass traveled to Rome to be with his father's extended family.

Cassius was at first welcomed warmly by his father's family, which was a successful military family. However, his mother's lineage as a Scot made him less of an Aurelius and more of an outcast. He tried his hardest to fit in with his cousins, and formed a strong bond with his cousin Darius Aurelius, who convinced him to join the Roman Army. It was during this time that Cassius learned to fight and live a warrior's life, something he found he had a talent for. More than that though, he really did best at planning and strategizing. While Cassius advanced in the Roman Army, Darius remained a footsoldier and died in battle, a loss that stuck Cassius hard. He ended up in what is now modern-day Southern Serbia, then called Moesia, along the Danube River.

He fell in love with both the region and the people there, and once he became established as a Roman officer, he married the daughter of a local man with political ambitions. Her name was Ariana. He loved her dearly, but just a few short years into the marriage, war broke out. Dacian King Decebalus crossed the Danube river and raided Roman cities in Moesia. In response, the then-Emperor of Rome, Trajan, ordered his troops across the Danube river and launched an invasion as part of his conquest of Dacia.

The battle lasted a year, in which Cassius was killed in battle, not just once, but three times. At first, he and his fellow soldiers assumed that the mortal wound was not as bad as first thought. But he couldn't deny feeling and perceiving things differently. Everything had shifted somehow, and he began to learn that he simply couldn't die, no matter how much he wished for it. Losing his wife and home and living with his fellow soldiers threw him into a deep depression, but he still forced himself to take part in the battles.

Finally, the Romans regained control of both Moesia and Dacia, and Cassius began the journey back to Rome. On his travels, he met a man named Naphtali from the East who informed him that he was indeed immortal, and that he could teach him what that meant.

Cassius spent many years training with Naphtali in Rome, eventually setting up along the coast. Cass served as advisor to the local government, and oversaw security for the region. He made sure Naphtali was sheltered from local troubles, and continued to learn his role in the immortal world.

As the Roman Empire began to implode, the two immortals went their separate ways. Cassius spent many years moving around, blending in easily wherever he went. He usually talked his way into the military, and his prowess in strategizing battles was usually quickly realized and capitalized upon.

He tended to stay in Western Europe or Great Britain, meeting many other immortals along the way - including the MacLeod clan. He often visited his mother's hometown in Scotland, even centuries after her death. He would keep track of his mother's family line over the years, keeping notes in a journal on those who'd moved away and those who died. Sometimes he would strike up a conversation with them as a friendly stranger passing through, but mostly he just liked watching from afar and helping them out anonymously when he could.

He married frequently at first though he was bisexual since that was a part of the culture in which he was raised, he was also raised with the belief that same-sex partners needed to be of lower social class, and female partners were seen as the appropriate life partners. So it was with that viewpoint that guided his relationships with both men and women. He tended to favor women as romantic and sexual partners and men as social and sometimes sexual partners, and rarely did the two overlap for many centuries. Sometimes the marriages worked out, but more often than not he would leave, not wanting to see the mortal women he loved die.

He went to America in the 1600's, and was a strong supporter of the Revolution, working as a British spy for General Washington for many years. It was a different thing for him to work covertly rather than openly in battle, but he found he had a knack for political deceit. He could be charming and played the loyalist, but it cost him in how he was perceived by others. He could not openly support the Revolutionaries until after the war was won, and by then, most of the damage of pretending to be a loyalist was done. He was growing used to living his life away from family, and kept most at arm's length.

He settled for many years in Baltimore, moving to Philadelphia and fighting for the Union in the Civil War. In Philadelphia, he rose to the rank of Captain, commanding a company (100 men) of the Union Army. There was talk of promoting him to the more strategic and administrative role of Major towards the end of the war, when a fellow soldier – a mortal Lieutenant Colonel – approached Cass, telling him that he knew what he was…because he himself was a Watcher.

Though it was highly irregular for Watchers to tell a subject immortal of imminent danger, this one saw the value in keeping Cassius well-informed and on the Union’s side. He explained that there had been a renegade group of former Watchers who felt that immortals were a threat to mortals remaining at the top of the human power structure, and as such had to be eliminated. These, the man explained, were Hunters.

Cass wasn’t sure what to believe at first, but after checking out some of the basic facts of the man’s story, he came to believe it was true. It pained him to leave his post at such a crucial time while the war was all but won at this point, there were still many battles to be fought and one to secure their position. He warned his informant that he’d be leaving but not where he’d be going, and with that, Cass headed further west, to Coshocton County, Ohio.

Once there, in an effort to keep a low profile, he turned to farming. He and a closely-knit group of farmers were settling and homesteading the west country, and he worked hard to learn the land and how to farm it best. It was stressful, but in rural areas he found it easy to stay hidden from Hunters and other immortals alike.

Between 1864-1875: Still, he hated the fact that Hunters existed. If it weren’t for being warned by a Watcher, Cass may well have been snuffed out by the Hunters. At this point, he sought to form his own organization – the Guardians. Like the Watchers, he started a network of like-minded peaceful immortals who, while still participating in the Game, sought to protect one another from mortal Hunters. His goal was to unite those immortals seeking Sanctuary and to provide immortal (rather than mortal) protection within its own network. He tried his best to stay under the radar of the Hunters, but he knew the Watchers knew about him. Cass approached the watcher who was once his superior officer, and let him know about the Guardian network, in hopes that they might one day unite Watchers and Guardians to share information. Sadly, this goal was never reached, as there was a lot of political back-biting amongst certain levels of Watchers. Cass ended up losing faith in Watchers as a potential ally – after all, the Hunters themselves started off as Watchers.

The Guardians existed as an underground network, but never took off without the support of the Watchers, and was very limited in its reach and scope. Often, connections between individual Watchers and Guardians were developed, but kept secret as they worked to warn immortals of specific threats from Hunters.

His goal was to unite those immortals seeking Sanctuary and to provide immortal (rather than mortal) protection within its own network. He tried his best to stay under the radar of the Hunters, but he knew the Watchers knew about him and decided to try and benefit by letting him know of the Guardians' presence, should they need help.

Over the centuries, his professions changed with every generation's needs. From shepherding to farming to blacksmithing to shopkeeping to antiques dealing to internet technical advisor and eventually, internet security advising for a top securities firm in Boulder, Cass has always kept himself busy.

He was in Boulder when the superflu hit, and he knew exactly what was coming from the dreams he had of Mother Abigail, with a dark figure constantly trying to break into those dreams. The old woman in the dreams warned him that if he was not ready to stand against the Dark Man, 'best you be takin' shelter in the mountains - those in town'll be needin' ya safe soon enough.' He took heed, knowing only that he didn't want to fall anywhere near the Dark Man's radar, and headed into the mountains on motorcycle. He was planning on going all the way up to Loveland, but was distracted by a quickening in Estes Park, where he met Becca Kirk.

Eventually, they met up with two other mortal men, and ended up at the Stanley Hotel. It had a prime view of the entrance to Rocky Mountain National Park in the distance, and also was set up to deal with living in harsh winter conditions. In short, it was perfect.