Leonardo de Vinci. He could have been trying to get attention of other time travelers saying hey I'm stuck back here. -u/Fickle_Penguin

Stanislav Petrov was a Soviet lieutenant known as "the man who saved the world." Tensions were riding between the Soviet Union and the United States, so on the 26th of September in 1983, he was on duty for a nuclear early-warning system. The system detected multiple missiles launched by the United States, but Petrov broke protocol, following his instincts by choosing not to report the danger to his higher-ups. The missiles turned out to be a false alarm, as he had thought, and, as Petrov's title suggests, he very well may have saved the world that day. -u/phosphoron

Edgar Allen Poe writes about an event 40+ years in the future. Basically, Poe writes about four people who are starving at sea, draw straws, and kill and eat the loser, cabin boy Richard Parker. 40 odd years later four people are adrift at sea in a lifeboat, one drinks seawater and goes into a coma. When they draw straws for who will be eaten, the coma guy gets the short straw in a development that surprises no one. And so the three other men kill and eat the cabin boy. Richard Parker. Seriously. -u/TuckerMouse

Cyanide Gas Attack Thwarted in Tokyo Subway. 20,000 people could have died but a worker found a burning gas bag in a toilet just before it mixed with another poisonous another gas bag - just in time - and put them out. That was in Shinjuku station. I was in that station that day, and that person might have saved my life. -u/Idkeepplaying

A Belgian businessman was instrumental to the Manhattan Project's success. Realizing uranium's importance, he shipped 1,200 tons of it to Staten Island. When Lieutenant Colonel Nichols contacted him, he simply responded: "You can have the ore now. It is in New York. I was waiting for your visit" -u/plopsaland

I would say there is significant evidence Fidel Castro. Every single assassination attempt failed, sometimes because of wildly miscellaneous circumstances, including a sabotaged diving suit that somehow got “miraculously switched” with someone else, who ended up drowning in his place. Dude holds the world record for over 600 attempts, I believe. -u/Demiscio

The commando raid on the Norsk Hydro heavy water plant in Hardanger Norway during WWII, the Norwegian commandos parachuted in during one of the worst blizzards on record, along with hundreds of pounds of explosives, and had to trek through the Norwegian wilderness for 15 days before they found a hunting cabin. The English commandos who were supposed to link up with got shot down, and the only reason they were able to make it to the cabin was that they found one of the commandos sled, which he had lost as a child. After that they had to hole up in the hunting cabin for months, waiting out the weather. They survived on moss until, on Christmas morning, one of the men managed to shoot a deer. They went on to destroy the heavy water plant as well as sink the ship carrying what heavy water had been produced, effectively ending any chance Nazi Germany had of developing atomic weapons. -u/Gentleman_Viking

When Andrew Jackson’s assassin attempted to shoot him, both of his flint lock pistols misfired. Andrew Jackson had to be restrained after almost beating the assassin to death with his cane. The two flintlocks were examined after the incident and found to be in good condition. -u/Two_Bears_HighFiving

During the war of 1812, seems like a time traveler with weather control capabilities started a freak tornado that effectively ended the British occupation of Washington. "More British soldiers were killed by the tornado's flying debris than by the guns of the American resistance." -u/Zeppekki

Tsutomu Yamaguchi. Survived both the bombings at Hiroshima and Nagasaki. Reads like a satirical time-traveler story where the protagonist screws up his dates. -u/OlympusJMoosecock

Eli Whitney, the guy who invented the cotton gin, helped cement cotton as a major cash-crop which drove even further demand for slaves. He, infamously, made no money off the development, as it was a simple and easily-copied machine, but cotton helped drive the economic growth of the South. Frustrated, he eventually abandoned efforts to profit off it and went into the industrial world, where he was a small contributor to the development of higher-precision machining and design (particularly for firearms). This in turn helped drive the growth of industry in the North, which was a major factor in giving the North the might and materiel to defeat the South. -u/SPOOFE

Franz Ferdinand's assassination. It was so much happenstance, shenanigans, and tomfoolery that it's like a special achievement in a hitman game. -u/RigasTelRuun

Tesla's AC Polyphase System. One minute, we're in the stone age of electrical distribution, and the next, Buffalo, NY is being powered by the Alternating Current being generated at Niagra Falls by Telsa's genius system. -u/randyfromm

The russian writer Fyodor Dostoevsky was sentenced to death by firing squad and just as they were preparing the groups to be shot, a messenger came with a letter from the Tsar “forgiving” them and the sentence was changed to prison labor. He later went on to write some of the most influential novels of all time. -u/smokeyman992

The American Civil Wars first real battle was at Bull Run on land belonging to a Mr. McLean. After that he said "Screw this, Ima move to the country and avoid this war". He moved to Appomattox Courthouse, VA where Lee surrendered to Grant...in the McLean's living room. -u/rgrtom

Mendeleev, who created the periodic table, was struggling to order the elements in a specific order/pattern. He then was able to order them like we see today after having a ‘dream’ where all the elements fell into place, even leaving gaps for elements that hadn’t yet been discovered. I know it’s not exactly a major historical event, but it’s been the foundation of science for over a century but when I first heard I thought it was a bit suspicious how it all fell into place. -u/willmac28

A book that predicted the sinking of the Titanic. Futility: The Wreck of the Titan. -u/sekscat

Isaac Brock's almost single handed defense of Upper Canada from the US invasion in the war of 1812. Canada doesn't exist today if not for a balls-to-the-walls British general in 1812 who in the span of 3 months single handedly raises an army, defends 750km+ of warfront, and cements two victories over forces than outnumbered him 3:1 to 5:1. -u/dbcanuck

I read a theory somewhere that this has essentially happened because The Simpsons has had 706 episodes as of today, and with that many episodes multiplied by the fact that each episode usually has at least 2 plots running- that's over 1400 different storylines. With the style of their show being satirical, it's just bound that they were going to predict some things along the way. But yeah, employing a time traveler on the writing team probably helps too. -u/TenseEye

I’d say the Battle of Midway. The major turning point in the naval war in the Pacific. The battle destroyed the single most powerful naval strike force in history and shifted the balance of power to the US. The actual course of events during the Battle of Midway was a series of near misses for the US until, conveniently, two separate air strike forces arrived at the same time to decimate 3 out of 4 Japanese aircraft carriers. Absolutely amazing providence. -u/QuantumInteger

The election of 1876. -u/lovesaqaba

I am almost certain Gemistus Pletho (1355-1454) was a time traveler. He proposed "a new constitution of strongly centralized monarchy advised by a small body of middle-class educated men. The army must be composed only of professional native Greek soldiers, who would be supported by the taxpayers, or "Helots" who would be exempt from military service. Land was to be publicly owned, and a third of all produce given to the state fund; incentives would be given for cultivating virgin land. Trade would be regulated and the use of coinage limited, barter instead being encouraged; locally available products would be supported over imports. Mutilation as a punishment would be abolished, and chain gangs introduced."-u/[deleted]

Jack Ruby clearly was sent to kill Lee Harvey Oswald so no one would ever discover it wasn’t him who killed Kennedy. -u/possiblyhysterical

Sometime between 200BC - 100 AD. the Ancient Greeks had invented a early prototype steam engine (Aeolipile). But they really didn’t give it much further thought. The Ancient Greeks were clever, but somehow, no one seemed to realize the potential of this invention. It never developed beyond being more than just a curiosity. Had these Ancient Greek designs been more widespread. There is a good chance the industrial revolution could have happened 1,500 years earlier. But honestly, it seemed like someone was intervening to prevent these designs from being disseminated. -bd_magic

When the Persians/Muslims were about to invade Europe, they were suddenly and inexplicably stopped as their invasion fleet fell to "Greek fire". Artists of the era made paintings showing a small number of "Greeks" destroying hundreds of ships with what clearly looks to be some sort of portable flamethrower. No one in antiquity had ever mentioned or used "Greek fire" before that event, and no one since has ever used it again. We still have no idea wtf it was, all we know is it appeared out of nowhere and stopped a monumental invasion. -u/Namika