Well we really dont know what angron could have become because of the implants that enhanced his beserk rage to ridiculous levels. However upon his landing he did rip the shit out of a load of eldar with his bare hands, and even before they became "world eaters" his legion were known for brutality and rage.
I always think that alot of the chaotic primarchs have there own loyal counterpart really, its an analogy that easily comes undone but a few examples in my opinion
All the primarchs as we see in the first heretic were essentially first and foremost meant to be killers, leaders in battle that brought worlds under the swell of the emperors rule.
I dont think the emperor had a specific purpose for angron, though he does to me represent the emperor's merciless unforgiving rage.
kudos to lillian thorne for the awesome sig