Oathbound of the Black Oak.
They pursue a foul priest of the Withering God called Shadowblight, who has done many an ill deed to the people of the world, and personally grieved each of the Oathbound.
Summoned together by the spirit residing in the Black Oak, they made an oath to catch the priest and exact vengeance on him.
But the priest's power is strong and his influence wide, they cannot assail him directly. Gathering allies and sometimes new enemies, they journey the land, visiting city-states and working for them, so long as the deed does not help Shadowblight.
Many a great foe did they fell, warlords and tyrants, slavers and wizards. Sometimes the nefarious path of the road becknoned to them, and they answered it's call. The assasination of a princess loved by her people, razing of the temple of the Sunlord, and plunder of countless tombs.
As they pursued Shadowblight, they were pursued as well. A cruel wizard they failed to kill, disfigured permantently by a blow to the face from a torch, chases after them with magical beasts, his burnt face appearing in the campfire, sprouting blasphemies at them. The king who grives for her assasinated daughter has posted a great amount of silver for their capture, which causes great troubles for the Oathbound, no matter where they go.
They even meddled in the wars between city-states, at times commanding small armies, sometimes stealing important resources.
Some of their most disasterous things include accidentally awakening a small host of swamp puppets that pillaged the countryside, of which our heroes took advantage of as well. But perhaps greatest of all, after burning down the temple of the Sunlord and taking the Eternal Sun from within, they managed to douse it, which made the Sun itself vanish from the skies, and for a month no one could see farther than a few meters without a torch. Ultimately they managed to correct their error, a set of deeds they saw wise not to brag about.
Rachne, a past middle-age woman who excels in both sword an sorcery, she who supports the group with her strength, of the Trunk.
While not physically too strong, her skill and experience at battle is her truest asset, both martial and magical. Her magic is mostly use of wind for strange purposes, buffetting her enemies away and blowing their spirits away with magic wind, leaving them in panic, as well creating magical walls and barriers out of many strange materials, both magical and natural.
The sacred ancestral relic of her clan was stolen by the priest and she is on a quest to retrieve it.
Her steady nature is the balancing nature of the Oathbound. More than once has she held Boarface in place when he has tried to do something that might otherwise become famously stupid. Where Rosamia might lapse into uselessness, it is her steadiness and resolve that endure until the troubles are over.
Rosamia, a priestess of the Withering God herself, was forced to sacrifice her husband and child to sate the apetite of her god, she became a renegade and swore vengeance. Hers are the Leaves, sometimes blooming, at others, withering away.
Strangely, she still recieves the blessing of the Withering God, but only periodically. Neither she or anyone else knows why, for as she has forsaken her faith, she should not be blessed anymore. Yet she is, which is a testament to the strange ways of her once deity.
Periodically causing great mischief and great aid, she is an unpredictable element in the group. When things are going very well, she might do something very foolish and ruin the day, yet when things look hopeless, it is she who solves the situation.
Fenster, a wily merchant and negotiator, as well as a dabbler in illusionary magic, he who provides for the group and is symbolised by the Roots.
His reasons are mysterious and his own, not even his companions know what drives him.
His abilities mostly lie in the non-combat area, befuddling foes both politically and enviromentally, allowing them to plunder many places without being seen. When forced to do battle, he misleads his opponents and conceals his comrades from sight to the best of his ability, for he is no match for even the worst of soldiers.
He is the one who most of the time gets our heroes out of trouble, both with his magic and his silvery tongue, and strangely enough, he is never the one to actually get them in trouble, despite his abilities in deception. His wisdom is that which holds the group in place.
Once a hero, a mighty warrior, now cursed to have the head of a boar, a deed done by Shadowblight to him in vengeance for him having slept with the sacrificial virgin and for having stolen relics of the Withering God. Known as Boarface, his domain are the branches, he who spreads influence of the group far and wide.
His brute strength, endurance and pig-headedness are the stuff of legends, and few who know of him(and almost everyone does) dare to challenge him, except the errant young warrior wanting to prove his worth by defeating Boarface. These challenges never end well for those who challenge him. Wielding the spear made from a branch of the Black Oak, a weapon he calls the Festering Death, and a huge sling which in his hands doubles as a siege engine, he is a truly terrifying foe on the battlefield.
When he was cursed by the priest, not only did he gain the head of a boar, but his apetites all grew. His greed for treasure, his hankering for food and his carnal needs all cause the party trouble where-ever they go, as if they didn't have enough of it. Laying with the daughter of the Chief of the Silver Hall, plundering his treasure and eating his famous white bull, is the most famous of his triumvirate of vice. But he is also the one to always save them from any physical trouble, whether it be strange monsters or fierce warriors of an enraged chief.
One day they will challenge Shadowblight directly, but for now they must bide their time.
(I probably forgot something, but likely nothing of huge importance. Obviously the heroes ultimately felled Shadowblight and his cult, dispersing after that. So in the scope of the game, they would still probably be on their quest to defeat him. Game system was a homebrew, influenced by the Conanic tales. The tale is slightly embellished to be a more fun read 
)
As for how they'd be incorporated, probably as a band of rampaging good-for-nothings who could be hired sometimes to do your bidding. Of course, simply killing them might yield some of the loot they have, which might be necessary if they decide to do something stupid.
