Bruno S. did not receive an Oscar nomination for portraying the titular character of The Enigma of Kaspar Hauser.
Bruno S.'s performance, as typical for a Herzog lead, is as a man that is either an extreme himself or in an extreme situation. This is the former for the strange man at the center of the film. This is not a film where we are meant to necessarily emphasize with the outsider, Herzog positions us technically closer to the view of the town's people trying to decipher the man. We are only given slightly more information then they are initially since we at the very least see Kaspar as he is in his confinement in a dank basement, and is taught some strange lesson by a man even more mysterious than Kaspar himself. The man leaves Kaspar in the town with the note, and teaches him to repeat a single phrase about becoming a gallant rider, and that is all. After that we are much like the town just trying to understand the man, and it is with this idea that Bruno S.'s performance is built around. S.'s performance is to give us the behavior, but only he is to understand it, not us. In the opening scenes, and his initial moment in town S.'s whole physical performance is of this strange specimen that we're are not expected to fully know. He grants Kaspar wide eyes that seem to take in everything around him, and his body language is distinct almost statuesque. He is a curiosity just from looking at him, which is exactly as Kaspar should be.
Bruno S. succeeds in being compelling just in himself as you watch there is just something about him that intrigues and captivates even beyond his strange note and past. This is essential to the character given that everyone becomes so interested him to the point they present him in a show despite there technically being nothing overtly abnormal about him physically. It isn't just the story though as S.'s performance also brings that strangeness so effectively to life. S. creates the sense that there is a mystery there even though he never tells you what it is. S. gives us a man who has been in an experience that does not relate to any other man in his state of this distance, but it is a certain type of distance that he expresses. S. is carefully not to be off-putting in the early scenes as his whole state of being has this naivety only to Kaspar himself. He's not exactly a child yet there is an innocence to him that makes it as though you not only want to learn more of the enigma even though S. gives you few additional clues through his own performance to what the man is.
The film has a time jump where Kaspar has learned to easily communicate at least verbally with others, however that in no way removes the mystery of the man. S. portrays the growth in communication is only to a point as even the way he delivers the lines still is more at others, or even to himself rather than with another. He never loses that certain stare of his that now seems to come less of a man who wishes to observe everything around him, but rather of a man whose sight is of some other plain. S. keeps the man as much of a mystery still not allowing you into his plight or to really emphasize with him. Herzog and S. instead keep you still with those around him attempting to decipher what is the story to this man. Every moment of S.'s performance keeps this self containment of the man is. When Hauser mentions his own views on things these are delivered bluntly just as almost random thoughts, and S. portrays these distinctive emotions of the man. He never emotes as a normal person exactly he almost emotes in this particularly intense yet still abrupt and remote way that again keeps him far from an attachment. The main different in the time jump even is that in a way Kaspar becomes less innately likable since now one knows he can communicate yet chooses not to. S.'s performance technically though is of the same man who has just the only difference was his vocabulary of words and knowledge of the world has grown. This is a idiosyncratic performance by Bruno S. as he just is as Kaspar should be. He purposefully is never quite relatable, instead S. gives a performance that succeeds in bringing to life a true enigma that is impossible to fully comprehend.