For canon information, see here.
"Only the asari, 'Equal voice and rights for all, unless we don't like you in which case we'll sic our biotic murder-priestesses on you.'"
- Nikolai Aleksanders (not the most pro-asari of commentators).
The Order and the Code
Justicars are never recruited or selected; when an asari is so affected by injustice that she cannot be satisfied by any conventional legal redress, she may seek entry to the Justicar Order, whereupon she undertakes long and gruelling training (it is accepted that not all trainees will survive), and forsakes all family, children, property, and any other connection to anything but the Code, which she must learn by heart.
Justicars travel with only their weapons and armour (which are of the finest quality, despite frequently being constructed in archaic styles to embody the long history of the Order), and in the course of pursuing criminals assigned to them (those the conventional justice system regards as too inherently destructive to prosecute by any other means) are duty bound to enforce the Code at all times, punishing the guilty and protecting the innocent wherever they become aware of an injustice. In their single-minded adherence to the Code justicars are capable of ruthless methods that would give even a seasoned huntress pause; however they also will not hesitate to lay down their life in protecting an innocent, no matter how inconsequential the circumstances may seem on a grand scale.
The Justicar Code is composed of over five thousand sutras, which define the just course of action for any situation a justicar may find herself in. Although justicars do not believe in variable interpretations of the Code, the Code itself gives certain avenues for a justicar to tailor her actions in response to circumstances; despite popular myth, justicars are not required to simply execute every law-breaker they become aware of. Even so, justicars are aware that their absolutist methods have the potential to inflict disproportionate harm on relatively minor offenders, and they take care not to investigate beyond the narrowly-defined parameters of their cases, enforcing the Code on those within their view but deliberately avoiding exposure to unnecessary provocations.
The Code is a document available to the public, and within the Asari Republics the Justicar Order is legally empowered to act in accordance with the Code by the democratically expressed will of the population. Most asari raised in Republican cultures view justicars in a quasi-mystical fashion and consider them nigh-infallible, or at the very least so unswervingly dedicated to their cause as to merit the carte blanche faith they are shown. Although any act of injustice falling within a justicar's notice demands action, regardless of the perpetrator or potential repercussions, the Order is primarily intended to address injustices committed by asari, and justicars rarely leave asari space except in direct pursuit of asari criminals they have been assigned to kill or capture.
The Justicar Order was all but wiped out during the Reaper War, though the few survivors are rebuilding their traditions. A surprising development has been the so-called Second Founding of Justicars, by asari ex-pats on the batarian world of Lorek, bringing the Justicar tradition, in altered form, to the Batarian Confederacy.
In Popular Culture
Pirating Gang Wiped Out By Justicar: One of the survivors contributes to clean-up on the Republics piracy issue.
The C-Sec Code: And here's Myrrick's experience.
Any of You Dealt With Justicars Before?: Myrrick recalls his encounter, people debate the relative merits of the First and Second Foundings, and more.
Diary of a Justicar: The Order posts updates to CDN, accidentally. There is, inevitably, argument.