Obscure lore: the hospitallers
The hospitallers are an Imperial fists succesor chapters formed during the 24th founding. Much like the black templars they are far from codex compliant and instead have only three companies that focus on defending the emperor people,to fight his foe and to stand vigilant against those who wish to disrupt the emperor peace while they also have Terminator elite outside of the three companies known as "the vigil", within the chapter they also have the position of senechal which serves to advise their chapter master.
Much like their name would suggest they are inspired by the knights hospitaller (despite wearing the Heraldry and colors of the knights templar) and like them they care a whole lot about safeguarding citizen and wounded soldiers, going as far as mercifully killing them to avoid them diying by traitors hand (as detailed in the short story "final duty").
They developed a feud with the iron hands after the defense of Fabris Callivant where the iron hands stole one of their dreadnought to save an astartes (in the end they didnt even use that dreadnought chasis by the way) leading to a confrontation between the two chapters. In this battle the flagship of the hospitallers "shield of the god emperor" would also be lost through unknown reason.
We also have few named characters
Mirkal Alfaran: their chapter master who commanded their forces during the defense of Fabris Callivant who is also fast enough to dodge bolter fire and can see the fate of a person by touching them (idk if its psychic ability or something else), also he wears a lot of purity seals
Augustine Alvaro: the chapter senechal whos sarcophagus was covered in drawing of his own deeds, sadly his chasis would be stolen by the iron hands and hes more than likely to be dead, this is the reason they have a particular feud with the sons of ferrus manus
If you wish to read about them they appear in the short story "final duty" and also in the book "voice of Mars"