10 Most Popular Conspiracy Theories

1. Lee Harvey Oswald didn't act alone (or possibly at all).
Perhaps only 9/11 comes close to matching the multitude of theories and interest surrounding JFK's assassination in 1963. Kennedy was shot while riding in a presidential motorcade with his wife in Dallas. Lee Harvey Oswald was fingered as the gunman in the Texas School Book Depository that day, but he was shot and killed just two days later, which created a great deal of suspicion. Also, witnesses claim they heard shots coming from a grassy knoll near the motorcade, creating the mystery of the second shooter. The CIA, the Mafia, Fidel Castro, and Lyndon Johnson are often listed as the masterminds behind the murder and cover-up.

2. Princess Diana was killed on purpose.
When the People's Princess was killed in a car crash resulting from overzealous paparazzi in Paris, the public demanded answers. It was hard for them to believe that such a compassionate, celebrated figure could die so senselessly, so it didn't take long for theories to surface about why certain people in power would want her dead. Some think she was pregnant and planning to marry her boyfriend, Dodi Al-Fayed (son to the owner of Harrod's and Paris's Ritz Hotel), and planning to become Muslim, which might've worried the British Royal Family, given her influence on the people. Others state that the family wanted her out of the way so that people would support Prince Charles's remarriage. There are also optimists who believe she faked her death to escape the public eye.

3. AIDS is a man-made disease.
Those in the scientific community generally believe HIV originated from a strain of Simian Immunodeficiency Virus found in western African monkeys. But when a group of 500 African Americans were surveyed in a 2005 study published in the Journal of Acquired Immune Deficiency Syndrome, over half of them said that AIDS was created by the government. Conspiracy theories about why the government might have created the virus ranged from population control to the weakening of racial minority groups and gay people. Some also say that there's a cure for AIDS being back held by the government for similar reasons.

4. The government was involved in 9/11.
This is currently the most researched conspiracy theory on the Internet. Theories abound about the role of the U.S. government in the events of September 11, 2001, but most state that either the Bush administration had previous knowledge of the attacks and didn't act or that it orchestrated the entire thing. Both versions center on the belief that Bush and company wanted to gain more power quickly and get the support of the people. It's been said that the World Trade Center towers came down as a result of planted explosives, that a plane didn't crash into the Pentagon, and that Flight 93 crashed in Pennsylvania because it was shot down -- a theory that was only fueled when Donald Rumsfeld accidentally said during a 2004 speech that terrorists shot it down.

5. Elvis never really left the building.
Many people believe that Elvis is still alive and kicking. There have been numerous Elvis sightings throughout the years and most people point to his incorrect gravestone -- it says his middle name is "Aaron," but it's spelled "Aron" on his birth certificate -- as the key piece of evidence that his death is a fraud. The reasons for the faked death vary between him wanting to get away from the public to him being put under witness protection by the FBI for being a drug informant -- a rumor started by him meeting with Nixon in 1970 and telling him he wanted to help eradicate drug abuse.

6. The 1969 Apollo moon landing didn't happen.
At this point, the faked moon landing theory has mostly been debunked, but there are still a few ardent followers out there. They cite altered pictures and videos, missing design blueprints, and faulty recordings as evidence of the forgery. One of the most popular reasons given for faking the famous moon walk is that the Kennedy administration wanted to win the "space race" with the Soviet Union and instill public faith in NASA. However, most Americans still believe that Buzz Aldrin and Neil Armstrong walked on the moon that famous day in July.

7. A UFO crashed in Roswell, New Mexico.
When ranch manager Mac Brazel came across crash debris near his property in 1947, he didn't know what to make of it and alerted local authorities. That same day, the Roswell Army Air Field sent out a press release that stated a "flying disc" was found; later, this was retracted and the U.S. military told the public it was a fallen weather balloon. This slip sparked a huge conspiracy theory about the government attempting to cover up evidence of UFOs and alien existence; some even say there were alien bodies found in the crash. Now the story is that the balloon was part of Project Mogul, the government's attempt to pick up on Soviet Union nuclear tests. As a result, Roswell has become a big tourist spot for extraterrestrial enthusiasts.

8. Global warming is a hoax.
Despite Al Gore's influential documentary and the beliefs of most scientists, some people believe global warming isn't actually happening. Sure, the fact that Earth's temperatures are steadily rising are irrefutable, but supporters of this theory believe it's due to technology created by those in charge for a variety of reasons -- keeping the public in a state of panic to maintain control and decreasing world population being two of the main ones. Gore, the United Nations, and Maurice Strong (a man heavily involved in environmental politics) are often named by conspiracy theorists as purveyors of the global warming "myth."

9. Shakespeare didn't write all those plays.

The most famous playwright in the world might not have existed at all. Conspiracy theorists have been debating Shakespeare's life for years, arguing that William Shakespeare was just a pen name used by a group of writers, which might explain why his signature varied throughout his career. Others think that he did exist, but that he was simply a figure for another person to write plays through, such as Christopher Marlowe, Sir Francis Bacon, or Queen Elizabeth I. The main argument against Shakespeare is the fact that he was uneducated, which seems rather elitist. Regardless, this theory still generates a lot of interest, ranking fifth in Google's conspiracy theory searches.

10. Reptilian humanoids control all of us.
This has to be one of the wackiest theories I've encountered so far. It was started by a 1999 book written by David Icke called, The Biggest Secret: The Book That Will Change the World. In it, he explains that most world leaders -- including quite a few U.S. presidents -- are actually shape-shifting reptilian beings from a different planet who start wars and are responsible for horrific events like 9/11 in order to promote fear and hatred, which gives them strength. Oh, and they're seven feet tall. Reptilian humanoids … who knew?

As silly as they can sound, there's something to be said for learning about conspiracy theories. They can offer totally new and unexpected ways of looking at events, even if you don't believe them to be accurate. And if anything, they at least suggest that as crazy and ludicrous as our ideas and beliefs feel at times, there's always someone out there who takes it one step further -- unless you're one of the ones who believe in shape-shifting reptilian overlords … sorry, but you might just take the cake.