Marshal
'Marshal is an old loanword meaning "Stable Keeper" that has developed through the ages to represent someone who rounds up other people.
This has been used in military contexts to represent field commanders, or in law enforcement contexts to represent agents of the courts and/or various varieties of bailiffs.
Warhammer 40,000
Black Templars
The Black Templars Space Marine do not follow the Codex Astartes organisation in that they do not have fixed companies and therefore the rank of Brother-Captain does not actually apply to them.
Instead they use the rank of Marshal as their closest equivalent for the commanders of their individual crusade fleets.
Adeptus Arbites
The Adeptus Arbites includes the rank of "Suffering Marshal", which is a playable career in Dark Heresy, representing those officers who go on detached duties in order to track down and recover Imperial fugitives, usually from worlds which are outside of Imperial jurisdictions.
3rd Edition D&D
Printed in the Miniatures Handbook, like many of the classes presented there, the Marshal is optimised purely for battlefield combat and doesn't perform really well compared to other PC classes.
As expected from professional soldiers, they are trained in all armour and in simple/martial weapons. However their base attack bonus is the same as Rogues and Clerics, and their Hit Die is decidedly average at D8 so they do not really count as front-line warriors.
What they do get in terms of class abilities however is access to team enhancing abilities: First in the form of Auras which will be explained in further detail below, as well as the ability to grant ALL of his allies within 30' an extra move action a number of times per day.
The Auras come in two formats: Minor/Major and you can have one of each active at the same time. Each Aura grants circumstance bonuses to the marshal's allies within 60' as long as they remain conscious, mobile and audible and the magnitude of these bonuses scale with the Marshal's level.
Minor Auras generally provide bonuses on characteristic checks, which often require the PC to know what he's expecting in advance to be of any use, so is therefore situational. But since the bonuses can be swapped freely it's not such a big deal.
Major Auras are far more sweeping, and grant positive modifiers to things such as attack rolls, armour class or movement speed. These are far more useful to your allies as in most cases everyone shall be able to benefit from them.
From the way the class is built it really needs to be used in much larger scales rather than small groups of PCs, otherwise the bonuses that the class provides could be more easily outstripped by a divine caster through buffing spells.