In 4th edition D&D, there are 4 official character roles: Defender, Striker, Leader, Controller. Each role is supposed to have a specific purpose within the party. I've observed that some of the roles have a clear, unified identity, while other roles seem to be a combination of multiple sub-roles which could potentially be separated.
The purpose of a striker is to deal maximum damage to a single opponent, and the powers given to strikers allow them to deal extra damage to a single opponent. This is the simplest and most pure of the roles. There is one clear purpose to the role, and one type of power which directly serves that purpose.
Actually, the description in the Player’s Handbook mentions that strikers also have powers to help them single out a specific target they want to attack. But in practice this doesn’t really seem to be a distinction, different strikers have a wide variety of powers that help them or inhibit them from attacking a specific target, or no such powers at all.
The purpose of a defender is to protect the party by absorbing the enemy’s attacks. Defenders have two powers to achieve this – the ability to force enemies to attack the defender instead of someone else, and high defenses to absorb that damage. This is slightly more complicated than the striker, since these two powers could mechanically be separated – you could have the ability to draw attacks without having high defenses. But it doesn’t seem like a good idea! If you have the ability to draw attacks, having high defenses is practically required, so really defenders have a single clearly identifiable focus.
Leaders have one purpose – to help out the rest of the party – and two sub-roles – healing and support (support referring to improving teamwork and making other party members more effective). In terms of theme, these naturally fit together as ways of helping out the rest of the party. But mechanically, there is no particular reason these two sub-roles need to be combined. It would work perfectly fine to have a character with healing and no support abilities, or vice-versa. The reason to fit them together is that both fulfill the leader’s purpose, so if you want to play your character as being the party’s support character, you would want both abilities.
Controllers are the real mystery. Controllers have strong area effect attacks, and the ability to place enemies under various conditions. What these two types of powers have to do with each other beats me. They don’t seem related in either game mechanics or theme. The controller role doesn’t seem very descriptive. When I see references to a class having “controller abilities”, I never know which type of power that refers to. The theme of the controller seems to be “the offense-oriented class that isn’t a striker”.
Maybe the purpose of grouping these powers under the controller role is based more on having a fair division of labor. 25% of the characters focus on concentrated damage, 25% on absorbing damage, and 25% on healing and support, and 25% on other forms of offense. By putting one of each role in the party, you know you have everything covered. If there were separate roles for area effect offense and true control, there would be five roles, and if players chose them evenly, then 40% of the party would be special offense. If 25% special offense is the right amount, then having 5 roles would lead to too much special offense and not enough of the other roles. So perhaps grouping multiple abilities under controller leads to a good distribution of classes.
This reminds me somewhat of Champions, where some of the classic roles were Brick, Martial Artist, Energy Projector, Mentalist, and Other. Other wasn’t very descriptive – it just referred to characters who had some sort of strange powers. You might have the power to control luck, or to turn into an energy-draining ghost, or to transform enemies into animals. It didn’t really say much about what exactly you were or what you did. But when it came to party composition, it was sort of fitting that a “classic” party would have a good selection of traditional superhero archetypes, plus room for one character who does something totally different, whatever it may be.
Next related post: Comparing Champions roles with D&D roles