Factions are huge in my setting, but they are also quite different in many ways from the AL presentation. For example, Onthar Frume started out as a harper, and friend to Leosin (this is the Horde of the Dragon Queen campaign, obviously). The players had several choices later on, that resulted in Onthar leading an expedition in the Chult region in search of an artifact that resulted in his death. They were then called in to retrieve his body (or part of it) for resurrection and, if possible, finish his mission.
They did this, but Onthar was a somewhat changed man post-resurrection, ultimately suffering a bit of PTSD both in the way he died (black dragon acid) and in being pulled back into life afterwards. A big part of this was to illustrate how resurrection, while possible, shouldn't be considered a simple solution to the problem of death (a common theme with my campaigns). Anyway, after being resurrected, Onthar was nothing like the jovial paladin they had first met and come to know, and became more of a dour extremist bent on exacting vengeance and bringing the light by force.
Thus the Order of the Gauntlet was born about halfway into our campaign.