This seems to be the opposite of what Manbearcat is saying,
I don't think so.
[MENTION=6696971]Manbearcat[/MENTION] suggests that the fighter is the paradigm of the defender (I agree). [MENTION=22779]Hussar[/MENTION] says that fighters, out of the box, make the best defenders (I agree). These two claims aren't inconsistent, and I think are mutually reinforcing.
Hussar also says that there was a tone to the writing of 4e which many read as prescriptive (eg "only fighters can be defenders"). Personally I don't feel, and never really have felt, that the books had that tone, but Hussar is not the only peson to think they do (eg Mearls talked about "only one way to play guitar").
Supposing that Hussar is correct, that doesn't contradict Manbearcat, who said nothing about tone.
On the issue of defintions of roles: roles are shorthand labels for the combat functions that can, by default, be served by playing a character of a given class. So the best way to work out what a given role means is to look at what characters who fall under that role have in common - which is a matter of mechanics plus effect of those mechanics in play.
For leaders that's fairly easy - they all have a strong encounter-power hit point restoration ability.
For defenders it's pretty easy too - they all have an ability to mark (or, in Essentials, a mechanically simpler version of marking called a defender aura), plus an ability to punish mark violation, plus good AC and hit points.
For strikers, what they have in common (at least up until Essentials) is mobility plus hitting hard. For most strikers hitting hard is expressed via a damage bonus, but for the Avenger is is expressed via advantage on the to hit roll. Essentials gives us the Slayer and the Blackguard, who are non-mobile damage dealers - they are labelled strikers, but in some ways are a new role ("bruiser"?).
For controllers, what they have in common is debuff. Pure controllers tend to have a good suite of AoE debuff/control (though some single target also eg the Invoker has a 15th level daily single-target domination ability). Secondary controllers (eg warlocks) tend to have more single-target control.
If you want to build a character who is a defender but not a fighter or paladin, you might look at other ways to mark targets and/or punish them for mark violation. Just looking at 1st level options in the PHB, a 1st level cleric can take the encounter power Healing Strike, which is not a bad power: 2W +STR damage, the target is marked for a round, and the attacker or an ally can heal. There is no punishment for mark violation there - just the default -2 to the enemy's attacks that don't target the cleric - but that is still a bit of defence. The same character could also take the paladin multi-class feat Soldier of the Faith which grants training in a skill from the paladin list (which has a good suite of skills that a cleric might want) and permits use of Divine Challenge once per encounter (which is the ability a paladin uses to mark and punish). Now we have a character who can heal and defend - not as well as a fighter or paladin, but not hopeless at it either.
I wonder at what point do the roles become so wide and encompassing of so many different traits that they essentially become kind of meaningless as reference points? That is what I have been saying about 5e, IMO there is so much customization that trying to match a class with a definitive role as was done in 4e is kind of pointless.
4e doesn't have a 1:1 correlation of class to role - fighters and paladins both include strikers (slayer, blackguard), druid includes leader (sentinel), ranager includes controllers (hunter).
But in any event, I don't see the question of "Does 5e have roles" as being a question about what role is each class. It's pretty obvious, for example, that the 5e fighter picks up the archer as well as the melee warrior. The question of roles, for me, is whether the build mechanics tend to channel PCs into one of an identifiable suite of default competencies.
I think this is similar to what [MENTION=6698582]yakuba[/MENTION] is saying - perhaps not identical, because I think if the competencies are not from and identifiable suite then we only have roles "after the event", as it were.
the Fighter in 4e could not really be primarily a controller
I have a 4e PC in my game who disagrees with this. The polearm fighter with Polearm Gamble, Deadly Draw, and 4 AoE encounter powers, plus Footwork Lure (boosted by Rushing Cleats) at will, plus a bit of mobility to get into the thick of things (Mighty Sprint in this particular case) is a controller. That fighter is a vortex into which everything gets sucked, and from which nothting comes out alive.
Monk as psionic felt forced to me
There was a very popular rewrite of the AD&D monk in an early-80s Dragon magazine (number 53, Sep 81). As part of the rewrite it gave the monk quite a few psionic abilities, with this explanation (p 9): "The new special abilities and powers presume that the inner strength of monks flows from the mind — that it is a sort of psionic power."
And there was already a degree of overlap between monk and psionic abilities eg body weaponry, catalepsy/suspended animation.
So I think the treatment of monks as psionic has a strong D&D heritage behind it.
Steeldragons is right. The roles are the classes. You want details, read the class descriptions and learn about what skills and abilities you can pick. The assignment of classes into another layer of roles is unnecessary, and wouldn't impact how you create a character.
I don't see the reasoning behind this assertion.
For instance, I have many times on these boards, in the past few months, seen someone reply to a complaint about the need to play a cleric that there are other classes - paladins, bards etc - that can supply the party with healing. There is a function -
healer, or as 4e called it
leader - that players of D&D commonly want a character to be able to fulfil, and there are multiple classes that can fill that function. But not all of them can. A fighter or thief is not going to make a very effective healer.
Likewise, if someone wants to play a ranged attacker some classes will suit that function - wizard, fighter, ranger, to name a few - but others will not. Barbarians and monks, for instance, don't tend to make especially effective ranged attackers (but might make for good mobile skirmishers).
Role labels are labels for functions defined by the overlap between mechanics and fiction. (In some RPG systems, there is no mechanical difference between, say, a ranged attacker and a mobile skirmisher - that's just fiction - but D&D isn't such a system.)
Not using the labels won't make people be any less interested in the functions, nor change the fact that not every class can serve every function equally well.