The Crimson Knights are a Successor Chapter of the Blood Angels known for their overall preference to cooperate with other Imperium factions and for their proximity and cooperation with a local Forge World.
The Crimson Knights have eleven Companies. Being a Blood Angels Successor, they have a Death Company, albeit small. The Death Company of the Crimson Knights is small due to the high Primaris content of the Chapter (in current rules, as far as I know, there are no Death Company Primaris, though I believe the Red Thirst rule applies to some of them). In addition, the Crimson Knights' 7th Company consists entirely of ex-Deathwatch Marines (the 7th Company is referred to as the Crimson Stalkers, or just Stalkers for shorthand) and has something of a friendly rivalry with the Veterans of the 1st Company.
Crimson Knights wear a rather standard armor color. Their armor is solid red with golden kneepads, pauldron trim, Imperial Eagle and pack exhaust; Captains follow this convention as well for base colors. Their Sergeants follow Blood Angels heraldry in that they wear black pauldrons with red trim. Their Apothecaries wear white in place of gold in their pauldron coloring, their Librarians wear blue and their Chaplains wear black. Their Lieutenants wear gold pauldrons with red borders..
The Crimson Stalkers wear mostly-black armor with pauldrons whose colors match their brethren from other Companies. The Stalkers prioritize Intercessors trained in the use of Stalker Bolt Rifles as well as Reivers, but the Company's makeup is somewhat diverse regardless. In addition, the Crimson Stalkers are used as a second layer of training for some Scouts who make it through their initial training in the 10th Company, certain Scouts picked out for specialized Stalker training and experience.
The Crimson Knights also have a close alliance with their local Forge World, Ragnarus Secundus. Their Techmarines are especially well-trained, and one can occasionally find a Techpriest or two traveling with a Crimson Knights army, helping to maintain their vehicles. On the topic of vehicles, the Crimson Knights are usually seen in infantry formations, using transports sparingly and almost never using Predators, bikes or Whirlwinds. However, being a Blood Angels Successor, they have an affinity for the various Astartes gunships and other aircraft available to them.