The roles of a Knight (by magnet)[]
In RvR[]
The primal roles
The Tank (aka charge leader)[]
I call Tank the Knight who leads the charge, in front of Barbarians. His goal is to divert the attention of the enemies, because they most often choose the closest target . Once he joines the enemy ranks, the Tank casts Areas or support Barbarians on targets, continually trying to get the attention until he can't hold anymore and heads back hopefully to be healed.
The few seconds the Tank diverts the attention should be enough for ranged allies to cast their own area spells. The current problem here is that most experience players simply ignore the tanking Knight because he presents a low threat.
The Defender[]
I call Defender is the "combat control"-oriented Knight. He is the closest thing to a Barb as he can be; he holds a lot of weapon damage skills, of points in Trip and Feint.
The Defender was really harmed by the reduction of strength contribution to damage bonus. As of now, his role is mostly supporting the group: protecting Mages, supporting Barbarians.
The Paladin[]
Finally, I call Paladin the kind of Knights who mainly tries to support his allies with buffs such as Deflecting Barrier. He is half-Warrior half-Conjurer. As it is, his capacity to do so is unfortunately very limited; very few area buffs are worth putting all the required points; most notably the good ones are Star Shields, Deflecting Barrier and Heroic Presence.
I think that aspect of the Knight, as a defensive class, should be developed more with more interest. Sitting in the middle of allies and casting all possible auras, with no points in combat control (Knock Downs, Dizzy, etc) because all are in auras, is extremely boring. This is because most auras aren't "sexy/useful" enough and have a high mana cost, which leaves the Knight empty (Conjurers and Warlocks could give the mana back; but they don't).
Actual Knights are hybrids[]
No sane Knight would go for only one of those, obviously. Actual Knights are a combination of two of those, because even at high-level they lack the points to have the three playing-styles at once (or they must make serious sacrifices which will limit them in their ability to play each role).
The Tank-Defender can offer much help to Barbarians once in the enemies ranks, because his combat-control skills will be a great help to Barbarians who skill for max damage.
The Tank-Paladin helps the other warriors charging with his area buffs; Deflecting Barrier helps Barbarians and Knights alike a lot when charging and limits the damage they receive. However, once in the enemy group he can mostly try to divert attention and support with damage, but not much.
The Defender-Paladin is the one who supports the ranged allies with areas, and stopping adventuring Warriors.
For each of these 3 combinations, some may be more oriented towards one of the primal types, for example a Tank-Defender may be more oriented "Defender". My goal here was just to set a few names I can refer to when making the suggestions to make a given role more interesting and fun.
Note about Hunts and PvP[]
I don't really talk about Hunts and PvP because a Knight is very limited there; obviously the three types work depending on what happens in the hunt. Most Knights who hunt are of the Tank-Defender kind. For PvP, areas not affecting the Knight are obviously useless (and even so, they take too much mana for PvP). However Regnum isn't about PvP but about big group fights.