Bruno Ganz did not receive an Oscar nomination for portraying Jonathan Zimmermann in The American Friend.
Bruno Ganz plays the "average man" who by chance runs into cinematic famous psychopath Tom Ripley (Dennis Hopper), who we meet as your average picture framer and art restorer, who unfortunately has some blood borne illness that appears to be terminal. In one of the original Breaking Bad performances, Ganz's average man is someone we meet in his way, which is already a bit more because Ganz is just a naturally interesting actor. There's just something about him that is never boring which is useful for playing a potentially "boring" part initially, because his Jonathan just seems kind of interesting even if he is definitely just average at the same time. Ganz approaches his early scenes well without any fuss, there is a quiet subtle sense of his condition in the certain underlying darkness as the man goes about his life, even if he often smiles and seems to be warm to his kid, his wife, there is the underlying sense of the man sensing his eventual death. His first action in the film is to instruct on the action of valuable artwork, and to specifically snub Hopper's Ripley, who is pawning off the work of a dead painter who is in fact alive in order to earn a greater profit. Jonathan refuses to shake Ripley's hand, which Ganz plays as very matter of fact of the man who scoffs as a man he has viewed as profit minded within this world where he clearly respects the art. Unfortunately for Jonathan this compels Ripley to finger him as a man ideal to perform assassinations, since he is dying, which he begins by spreading rumors that his illness may be worse than it is.
Re-watching the film again shows the brilliant choice of Ganz to move from subtly to overtly shake the notion that Jonathan is a good man turned astray due to circumstances. Ganz performs this quietly in the scenes leading up to the first kill where he is asking both his personal physician, and a specialist, set up by the men who want him to perform the hit, about his condition. The scenes of the doctor have Jonathan prodding the doctor about the truth which you could take as a man needing to know the truth, or wanting to find a way out of the proposition, the specific kind of urgency Ganz portrays isn't as anxiety related to potential guilt, it's a need to support the notion of taking on the hit. Ganz presents a want for honesty, which he supports further even in the moments of being asked, where Ganz portrays surprise and disbelief however with a hint of interest that goes way beyond any kind of desperation. And while you may believe this is the innocent man turned astray, Ganz doesn't make it so simple in the story of Jonathan. Ganz is absolutely stellar in the first hit, because he doesn't portray it at all like a professional rather a man trying to be one. He labors moments of his movement, his choices are always telegraphed in the right way, because Jonathan is telegraphing themselves to himself. Ganz brings the right sense of the tension of the moment, again not so much the man facing the life or death decision but rather the fear of being caught and really even the tension of a kind of excitement as he goes about killing this man. With the key moment being after he makes his escape, Ganz's shows after the release of adrenaline a genuine exuberance of a man living as he kills.
After the initial killings one can take it as though the man is having second thoughts as we see him wallowing in frustration, though again I don't think Ganz plays it as simply as just a basic guilt for his actions. Rather Ganz depicts more so this frustration as he attempts to sink back into his normal life, a frustration though that less reflects a sadness for losing any kind of calm, but rather being stuck away from this experience that seemingly made him live again after being stuck within that certain confined state created by the idea of his impending death. When asked for another killing, Ganz's performance again delivers the sort of semi-no's as with only enough believability of a man convincing himself that he's not a killer, but far too weak to actually not continue on as he's tasked with a more difficult killing involving several gangsters on a train. But before that, it is essential to talk about Ganz and Hopper as we see Ripley's relationship with Jonathan develop, past that opening hostility. The subsequent meetings find Ripley quietly charmed by Jonathan's devotion to his craft, even his ability to spot that something was off with the painter's new work, and beyond that initial dismissiveness, Ganz beautifully plays a quiet relent on his earlier behavior even if he explains himself. And Ganz brings such a natural sense of the quiet joy in Jonathan as Ripley speaks so highly of him, Ganz portraying not as standard ego, but rather the needed boost for a damaged ego of a man looking for someone, anyone recognizing him as more than just some dying schlub.
Their relationship goes beyond admiration of craft as in the middle of the attempted killing on the train, Ripley joins Jonathan in his quest...and what we have is just a truly outstanding scene. The scene is just outstanding as it is thrilling, but also darkly comic at the same time. The essential ingredient to all of it however is the chemistry between Ganz and Hopper, because after the initial surprise Jonathan and Ripley become true partners. The two are wonderful in every interaction, despite being the unnatural habit of maneuvering murders in a very populated train, are so naturalistic in the way they create the tension but also share such a sense of joy in every maneuver. Both actors show that not only are the men loving it, they're specifically loving doing it together. Every moment is so much more because Ganz and Hopper accentuate every glance, every line, with such a deep sense of this very peculiar yet all too tangible camaraderie. With the finale of the scene being absolutely perfect as Ganz again brilliantly shows the true nature of this endeavor, not of desperation for money for his family as he dies, but rather a man who believes he is dying finding this outlet for living. As we see Ganz stick his head out the train car, and there is such sublime joy and exuberance of a man embracing life...even if it involves killing. Ganz and Hopper's chemistry is so fascinating because as truly bizarre as this friendship becomes, it is genuine in their way with Ganz showing the way he looks at Ripley giving him life, and Ripley in turn, oddly enough, seeing a genuine friend.
Ganz's performance throughout the final sequence of the film conveys the strange state of the man as he goes down this dark path willingly, even when his wife finds out, Ganz's performance brilliantly underlies the truth of the situation, as Ganz doesn't present the shame of a once innocent man who has to admit to his wrongdoing, rather he reacts more so like a drug addict whose fixation has been discovered. Ganz's performance reveals the man as recognizing this as a choice to do what he has done not just for the sake of it. The whole final sequence is amazing work by Ganz as he manages to do two things, one is run with his chemistry with Hopper, where the two seem complete partners now as they play off each other, but also show the man in his dying state of mind, to the point he's quite directly losing his mind in this kind of mania. In each successive scene Ganz's reactions become that much more extreme, and even distant, the moment he starts singing the Beatles even though Ganz makes entirely natural, by funneling into granting a sense in the unnatural state of Jonathan's mind as he's dying but kind of just living out his dying breath to what he sees as the most. The role of the man Ripley manipulates to crime I think could easily be completely overshadowed, and would be in the inferior re-adaptation of Ripley's game. While Hopper's amazing and often dominates, Ganz is never lost or forgotten in their scenes together by making this choice to not turn Jonathan into some random innocent, but a man who releases his darker self on his own accord in order to embrace what he has left of his life.