Seth was the only child of the head of a relatively affluent clan in Triscot, though not one of the most affluent clans of that village. Unlike with most wealthy clans, there was no single most important business for which his clan was known; all members of the family chose their own paths. In fact the clan was never as close-knit as many of The Land's most prominent clans, especially those of Triscot. The true cumulative wealth of the clan can only be guessed at, as individual members of the family tended to hold on to their own money, rather than pooling it. They also tended not to live on a single estate, which meant that very few of the individual homes of the clan's members were large enough to be considered estates at all, though most of their homes were surely more lavish than most individuals could afford. (This was especially true of those members of the clan who moved to other villages, where there tended to be less wealth per capita.) However, the most expensive of what few estates the clan did have was in Triscot, and belonged to Seth's parents. When they both died in 891, when Seth was 14, they willed the estate to Declan's younger brother, Grigory. This upset Seth, who believed the property should have been his. He had, in fact, never appreciated Grigory's presence in his family's manor, believing his uncle should have long since moved out. But Grigory ran his own accounting firm out of a wing of the manor, and often had a good deal of his clients' money on hand. He always said their manor was the safest place he knew, and he owed it to his clients to keep their money as safe as he could.
Seth of course received a considerable inheritance of his own, and would have been entirely welcome to stay in the manor as long as he liked, but he had no interest in living there with his uncle. So he took his money and moved to Plist, where he had no other relatives. As he was still young and hadn't yet completed his education, he hired the best masters he could find in his new village to teach him, before finally growing bored. By the time he chose to put an end to his formal education in 895, he surely could have started any sort of career he wanted, and no doubt would have soon distinguished himself. But he had no intention of starting anywhere but the top of whatever career he chose; he felt it would be beneath him to have to work his way up. Unfortunately, over the last few years he had spent most of his inheritance, and it would be impossible to start his own business, now. He resented the fact that he was in this position. He resented the prominent business people he saw all around him in Plist (at least in the sort of places he typically deigned to frequent). He resented the success of the rest of his clan, who he no doubt could have appealed to for help, though he felt that would be beneath him, as well.
And so his thoughts turned to those who truly were beneath him, socially speaking. It occurred to him that if he couldn't afford to start his own business, perhaps he could afford to buy his way into an established business, even if it wasn't a prominent one. At least he could start at the top, and he didn't mind working to build the business up to greater heights than it had known before he took it over. Unfortunately, any businesses he saw as acceptable candidates weren't actually on the market. Finally, he lowered his standards even further. Toward the end of 895, he bought the leadership of a local street gang called "Grey Skies." This meant not only paying the old leader to retire, but also paying all the gang's members to accept him as the new leader. They all apparently saw it as a joke, because that simply wasn't how gangs worked. They found it even more amusing when they learned what he wanted to do with the gang: he wanted to turn it into a business. But in fact, it was essentially business as usual. Aside from renaming the gang "The Greys," Seth didn't really want them to do much that was different from what they'd always done. He still wanted it to be a gang, even if it was run in a more orderly, businesslike fashion. Many of his gangsters began to think of themselves as "land pirates," a description Seth allowed, though he didn't exactly care for it. Meanwhile, his main goal was to make the gang more upscale; to steal from and deal to the upper classes of society, rather than the lower classes, which is what most gangs focused on. Trouble with the upper classes tended to garner excess attention from the police. However, Seth was careful to pick and choose which people he helped and which he hurt. There were plenty of wealthy people who were willing to deal with him, if they wanted goods or services they couldn't normally come by. And for his services he charged not just money, but their influence with the authorities. This way, when the ones from whom he stole made a fuss, the ones who were on his side made sure the police didn't work too hard to appease the concerns of those he'd hurt.
Over the next few years, the Greys grew in prominence, and eventually they only had one rival left in Plist: the Chieftains, who were led by Don. In 899, around the time that Don became one of the founders of LandOrder, Seth became one of the founders of InterGang, after being approached by a woman named Amelia with the idea of forming an inter-village gang. (Years later, it would be learned that the forming of intervillage gangs was actually part of The Plan, which led to the Coming of the Order.) Amelia's idea greatly appealed to Seth, who now sought to extend his reach beyond just Plist, into villages where his various relatives lived and did business. (Most especially this included Triscot, though that village wouldn't acquire an InterGang branch until 904.) So, the Greys became the Plist branch of InterGang. Meanwhile, the name for the head of a village's gang went from just "leader" to "don," in honor of Don of LandOrder. It's not fully understood why InterGang and other, smaller gangs chose to accept this practice, but they did, and therefore Seth came to be the don of his branch of InterGang. This is reportedly one of the things he hates most about his LandOrder rival, though he surely has many other reasons for hating the man. Thus began a rivalry that most people see as being entirely in Seth's mind; almost everyone in both gangs is under the impression that Don doesn't take Seth very seriously at all. This is perhaps partly due to the fact that ever since 899, many people have reported that Seth began acting more erratically than he had ever done before. Many people, both in InterGang and LandOrder, began to see him as a fool... albeit one whose ideas turned out well as often as not, regardless of how foolish they might have seemed at first. In any event, he had the trust of his capo, Amelia, much to the annoyance of some of InterGang's other dons, most notably Larami Illuminatus.
In 899, when both InterGang and LandOrder were established, Durell sent out Sorreters to various gangs around the world. It was the idea of one Sorreter, Merv, that Sorreters who wanted to join gangs (and could not possibly do so in Sorret, due to the efforts of Drag), should join gangs in other villages, thus helping the gangs stay in contact with each other, through t-mail and translocation. Merv was the first Sorreter who Seth ever met, and he asked Merv to introduce him to Durell. Though Merv eventually ended up becoming First Sorreter of LandOrder, Durell himself had no preference for any one gang over another; they were all just tools, to him. But in the early days, when the gangs were still working out details, it was often unclear who would join which gangs. Meanwhile, Seth did meet with Durell, and made a deal with him, the details of which are still not entirely known, though part of the truth did come out in 912.
In 904, when the surname law was passed, Seth's uncle Grigory chose the name Manager, as he was by that time the manager of a chain of banks. He was also the head of his clan, ever since Declan had died, and so the rest of the clan took the name as well. That included Seth, though he had little if any contact with his clan; their being such prominent members of the villages where each of them lived, it wasn't hard for him to find out what they'd begun calling themselves. It's unclear if Seth chose to accept their surname as his own out of a sense of spite, or of wanting to irritate his relatives (who surely wouldn't want to have the same name as a gangster), or out of respect for his late parents, who also would have been named Manager if they were still alive; or perhaps he simply chose it because he thought of himself as his gang's manager (particularly as opposed to being its "don").
In 912, Don took an interest in a group of adventurers and would be rebels calling themselves The Chaos, and this led Seth to take an interest in them, as well, thus increasing LandOrder's own interest in them, and also bringing the group to the attention of the police. The events that followed eventually led to the Chaos War; while it is most likely that this war would have happened with or without the involvement of the Chaos, it's unclear how it would have turned out. Therefore, wittingly or unwittingly, Seth Manager had an important effect on world history. However, not long before the start of the war, he disappeared, and is assumed to be dead. Details of his death or disappearance are unknown, though it may be related to his earlier deal with Durell, and possibly secret deals he made with others, over the years. It's also widely believed that he was a member of The Cabal, though that has never been conclusively proven. It is, however, known that he had clandestine dealings with Magistrate Lucrezia Nearwright, who is also believed to have been a member of the Cabal.