Idris Elba did not receive an Oscar nomination, despite being nominated for BAFTA, a Golden Globe, and winning SAG, for portraying the Commandant in Beasts of No Nation.
Idris Elba plays the leader of a loose group of soldiers who come across Agu. Elba, from what I have seen, had failed to really find his footing in terms of his cinematic output, delivering often forgettable work, though to be fair in rather thin parts. The commandant finally seems like a substantial role, and Elba seems to relish in the chance in his portrayal of the part. In the earliest scenes of the film Elba plays the part in a fairly grand fashion. Elba plays him less of a military commander and more that of a spiritual leader of sorts who marks his pardon upon Agu, acting it as though he is his savior. Elba is very good in these scenes bringing the needed charisma to the role that the Commandant can control his men without question at this point. He brings the right quality to his performance as he makes the Commandant seem something more than he is to Agu at first, as he makes himself to be the true leader of these men, that goes beyond even an idea of his rank. Elba creates a sense of benevolence in the Commandant as he treats Agu, and the other soldiers, with this essential warmth, as though he only wants what is best for them, despite the fact that he's actually just using young boys for his own ends.
A pivotal moment for Elba's performance comes when he forces Agu to murder a completely innocent man for him. Elba is terrific in the moment as he makes the persuasion believable for Agu, as he suggests to Agu that he is someway avenging his own family by doing this. Elba is chilling though in the moment though because he projects a disarming affection towards Agu, as he makes him do the ultimate act of hate. Elba continues to be very effective in being the father to all of his men in quieter moments, such as where he tells the men of the women in the next village he intends to conquer, as though he's telling them of a treasure they will obtain if they continue to follow them. My favorite moment his performance is a larger one as he primes his troops just before they enter into the fray of battle. Elba makes this moment as though the Commandant is firmly a man in his element, as he truly seems to becomes the men's spiritual guide as he leads them in a dance, as a for them to enter the battle. Elba properly rules the scene as he seems to become more than a man before his troops, as leads the men into the battle as though it is some sort of divine march, and he has become God.
Of course the commandant is not God, or a god, he's just a man, and not even much of a man. Elba does indicate this well even in the early scenes in the moments after the first attack, where the commandant finds some possessions to call his own. Elba makes him frankly a bit childish in the moment as though he's enjoying the power of his position a bit too much, he does not call it his own as a grand decree, but more of saying "Hey cool, that's mine". The cracks in the commandant's facade only grow deeper as the story proceeds, when the commandant indicates that he too must follow orders. Elba reveals just a bitter pathetic man who hates being reminded of his own position. This leads to an underdeveloped element in the film where it is heavily implied that that the commandant sexually molests Agu. The moment just seems to be there to be another horrible thing Agu is forced to do, but the way its done it feels like it's there to be a checklist without really having much purpose other than having the commandant being even worse than he already was. The commandant's fall only continues when he meets with his superior, and is treated with very little respect. Again Elba does well enough in showing just the angry thug beneath it all, as he lashes out for being treated as something unimportant.
The film continues along the path of the commandant's own self-destruction, and any sway he might have had over his men only evaporates as time goes on. This is as the commandant does anything to stay in power, including having his second in command killed, and then proceeding to basically have his men keep fighting even though they're no longer part of any army. The film does not really allow Elba to gradually depict this descent in the commandant as the film moves aimlessly for awhile, though not in a way reflective of the aimless way the commandant is using his men. Elba does not have much screen time after the commandant goes renegade as we just eventually find his final scene where the men finally rebel against him. To his credit Elba is good in the scene as he portrays with such exasperation the commandant's final attempt to keep control, but really has not charisma left as he still tries to command them to do his bidding. This even is handled rather swiftly as the commandant barely gets a final glimpse before the film cuts away, and we never see him again. One could take this to show how far he's fallen, as the man who was the center of all these men's lives is just tossed away with only a few words. The problem is it just does not build to this in a particularly engaging way, and once again Elba seems often underused. This is still a very good performance, a great one in the earliest scenes, but as the commandant loses power so does Elba's performance. Now one could argue that as intentional, but the portrait of a man losing that power isn't made especially compelling by the film or Elba. I don't want to sound too negative though, since like the film, Elba's work is tremendous in the beginning, but like the film loses that strength as it continues.