Aggro, hate, threat, whatever term you prefer to use for the unpleasant attention of monsters, is a fundamental part of MMOs. Let’s assume for a minute we’re stuck with the class system (as in character classes, not the struggle of the proletariat and bourgeoisie). At a basic level, you probably have a tank, healer and damage dealer. The tank holds the aggro, the healer heals the tank, the damage dealer… anyone want to take a guess? Award yourself ten points if you said “deals damage”, five points for “flounces around for a bit then turns up after the hard work is done to shout ‘MY KILL'”, and if you said “pulls the aggro off the tank, uses up all the healer’s manna in a futile attempt to keep him alive, causes a wipe, then insults the rest of the group for not doing their job and quits in a huff” then award yourself a stiff drink and a bit of a lie-down.
(Disclaimer: I invariably *play* damage dealing classes, I’m allowed to say stuff like that.)
Obviously there’s a lot of variation: other roles such as crowd control and buffing/debuffing might be performed by dedicated classes or combined in others; damage dealing often comes in ranged and melee flavours; hybrid classes perform multiple roles with varying degrees of efficiency; some classes may have pets to perform other roles, etc. etc., but at the end of the day, some classes are designed to be better at surviving the attention of monsters, and part of the game is to make sure they’re the ones being attacked, rather than the squishy types standing behind them.
This is where things get a bit tricky. Due to class balance, the better a class is at soaking up damage (or avoiding it), the worse they have to be at other things (typically dealing damage). This makes the typical MMO tank a peculiar beast without many parallels; the tank from whence they got their name, the armoured fighting vehicle, is heavily armoured, true, but it also has a socking great gun for shooting stuff (momentary diversion for tank grognards: granted, you can find some better examples if you really try, like the early WWII British Matilda II, with very heavy armour and comparatively poor firepower, but never mind).
Lack of damage means tanks need another way of getting and keeping the attention of mobs, often some form of “taunt” or “provoke” ability to gain extra aggro. Other classes may have specific abilities to reduce aggro caused by their own attacks/healing, or may just need to consider their own actions slightly more carefully (like waiting until the tank has stormed into combat before drawing too much attention to yourself). This works as a game mechanic, especially for giving the damage dealer a bit more to think about than how many buttons he can press to inflict indiscriminate havoc and devastation upon the surrounding area, but it can seem very artificial; how does aggro reduction work, are you pointing behind the mob shouting “Look! Behind you! A badger, with a gun!”? Is the tank’s taunt something like “Your mother was a hamster and your father smelt of elderberries!” while tapping his helmet in a strange fashion? One of the best analogies I remember is someone from the City of Heroes boards, likening being a Tanker to sitting in an armoured dustbin getting beaten by mobs, occasionally popping your head up to shout “YO MAMA’S SO FAT!” at them to keep their attention. It’s even more of a problem trying to adapt this system to Player versus Player combat, where you can’t force players on one team to attack a certain player on the other without some fairly extreme intervention (like the tank’s taunt rendering the opposition unable to target anyone else).
As per usual, I’ve no real solution to the situation, though in writing this I have realised if any MMO includes a “French Taunting Knight” tank class who gets to shout “You don’t frighten us with your silly knees-bent running around advancing behavior!”, I’m playing it in a shot…