The Omniscient Hero is not merely The Omniscient, he is ALSO a main character! This has a huge impact on the plot, because it means that the readers/viewers will either know exactly what's going on or they will not know what the hell the main character is really doing.
Essentially, a being who possesses enough relevant information to make the events less interesting or less believable. Such a being who makes any kind of deceptive plan useless by seeing through them all is likely to fall into this trope.
When an Omniscient Hero is faced with a Moral Dilemma, the problem is made much less complicated by the fact that he or she somehow...
- Has a flawless overview of everything relevant to the situation,
- Knows exactly what options are available, AND
- Knows exactly what the consequences of each option will be.
Theoretical moral philosophy is full of thought-experiments based on these three premises. For the protagonist of such a theoretical thought experiment to become an Omniscient Hero, the Moral Dilemma has to be transformed into a story and played straight. However, a Strawman Political or Straw Vulcan is very likely to mistake themselves for an Omniscient Hero, and then be very surprised or go into denial when it turns out that there was at least one of those three premises that he or she did not live up to.
Such a villain is likely to take their delusion one step further and also believe himself or herself to have a Omniscient Morality License, thus making it easier to convince themselves that Utopia Justifies the Means. Either that, or one turns out to having been a Straw Hypocrite all along.
- Adrian Veidt fits this trope. He has everything so well figured out that the morality issue is reduced to whether or not the goals he achieved were worth all the lives he sacrificed. However, two of the last few scenes make the whole thing ambiguous, leaving it to the reader/viewer to decide if the trope is played straight or subverted.
- In the same story, Dr. Manhattan himself WOULD fit the trope perfectly if it wasn't for a certain loophole that effectively make him lose his omniscience halfway through the story. Before that point, he is so omniscient that it bores himself, but the readers/audience is spared sharing that boredom since he's a side character rather than the protagonist.
- In the Swedish comic Bamse, the Lancer/Professor character Skalman often fit this trope. This is done intentionally, since the target audience is rather young and the use of a BOH lets the writers introduce relatively complex concepts without making the plot overly complicated.
- Batman in many modern interpretations is so Crazy-Prepared that he occasionally falls into this category. (The man has backup plans for the contingency plans of his backup plans!)
- Captain Mar-Vell's son acquired "Cosmic Awareness" like his father, but to a much greater degree — he literally knew everything that happened or could happen. It drove him mad.
- In The Incredible Hercules, during the Chaos War storyline Hercules was granted omniscience. Turned out to be practically worthless because Hercules either didn't bother to use it or purposely ignored it constantly making things worse. Only changed when all of his allies called him out on his crap and even then he had to be guided by others to victory.
- Nemo, the titular Mr. Nobody, is a rare sympathetic example. He can remember and envision all his possible futures, and it is explored quite well what this means for him.
- Haruhi Suzumiya's Nagato Yuki is one of these.
- The Kwisatz Haderachs, Paul Atreides and his son Leto II in Dune. Both of them come to hate this because it makes life so utterly boring when you know everything that's going to happen long before it happens. Everyone else comes to hate this because when someone is omniscient, they're effectively invincible: they know everything you're going to do before you even think of it, so no matter what you do, you're playing into their hands.
- In State of Fear, Professor Kenner already knows or suspects the entire plot of the bad guys at the start of the book.
- In The Wars of Light and Shadow, Arithon s'Ffallen, Master of Shadows, has inherited the foresight powers of his s'Ahelas mother and the empathy of his s'Ffallen father, which means that he sees the implications of all his actions, and feels the suffering they cause. The only reason why the Wars of Light and Shadow haven't ended with his suicide is because he has sworn an oath to survive at all costs, as his survival is critical to returning the Paravians to Athera.
- In Horns, by Joe Hill, the main character has horns growing out of his head that not only cause the characters around him to reveal their darkest thoughts to him, but also give him the power to see their entire pasts simply by touching them.
- Ia in the Theirs Not to Reason Why series is a somewhat unusual example. She can't "just" see her own timeline, she can see all of them. This also makes her an interesting case because while she could theoretically prepare for every single way events can play out, she doesn't actually have time to A) look through all potential outcomes of a situation and B) set up contingency plans for all of them. This leaves her immensely powerful, but Not So Omniscient After All because she can never be sure which of the many possible futures will actually happen in her part of the multiverse.
- Doctor Who: The Doctor has elements of this Depending on the Writer. He is easily the smartest person in the room, and can work his way out of just about any situation, up to and including the end of the universe. With certain exceptions. Notably, several episodes have the Doctor working out how to kill the enemy of the week within a few seconds, but either something happens which he didn't plan for, and he has to play a game of Xanatos Speed Chess, such as "Remembrance of the Daleks", or he's desperately searching for a non-lethal or more peaceful solution, which he sometime finds ("The Beast Below"), but often doesn't ("Warriors of the Deep").
- John Doe of the eponymous show has encyclopedic knowledge of everything humanity has learned up to the beginning of the show. He's also capable of easily using that knowledge, such as becoming rich in the pilot by playing the stock market, and countering moves in an obscure martial art. He's also an Omniglot, as demonstrated when he speaks Khmer to a group of Cambodian fishermen who rescue him.
- Theresa from the Fable series has the ability to see into the future. In Fable II and Fable III, if she hadn't been there to guide the hero towards their destiny, then there wouldn't have even been a plot.
- Dominic Deegan decayed/developped into one of these by the time of the Snowsong arc.
- Homestuck has Terezi. However, her ability only activates when the wrong choice will create a doomed timeline. Since attaining god tier, Rose is one too, though there are some ill-defined limitations. Jade also knows an awful lot after becoming a First Guardian.