© Getty Images

Jimmy Hoffa -

Jimmy Hoffa was a famous union leader in the 1960s. He was the president of the Teamsters, one of the biggest unions in the US. He was also known to be corrupt and ended up serving a prison sentence for his involvement with organized crime.

© Getty Images 

Jimmy Hoffa -

A few years after his release from prison, he disappeared. He was last seen at a Detroit restaurant where he was supposedly meeting two organized crime bosses. It's been established that he was killed by the Mafia on the day of his disappearance, but his body was never found. Numerous tip-offs have proven fruitless, and his burial site remains unknown.

© Getty Images 

Wolfgang Amadeus Mozart -

The great Austrian composer died when he was only 35 years old. He became ill in September of 1791 and eventually became bedridden with symptoms like pain, swelling, and vomiting.

© Getty Images 

Wolfgang Amadeus Mozart -

He was desperately trying to finish his masterpiece 'Requiem,' but he died in December before it was completed. As was customary at the time, he was buried in a mass grave. A gravedigger later claimed he had buried Mozart and could identify his skull, but tests on the skull were inconclusive.

© Getty Images

Leonardo da Vinci -

The great Renaissance artist moved to France in his later years, where he died at the age of 67. It's believed he was buried at his local church in Amboise, but this has been tricky to verify.

© Getty Images 

Leonardo da Vinci -

The church of Saint-Florentin was ruined during the French Revolution, and it was decided to demolish and rebuild it. Sixty years later, an excavation uncovered some human bones and a chunk of stone that had a couple of letters from da Vinci's name. It's been proclaimed that the church is his resting place, but there's no way to confirm.

© Getty Images

Alexander the Great -

Alexander the Great was one of the most significant emperors and conquerors in history, but he met a rather feeble end. He suddenly became ill after a feast and died at the age of 33. It's speculated that he may have had an illness like malaria, or was poisoned. He was buried in a tomb made of pure gold. Needless to say, it was looted until there was nothing left.

© Getty Images 

Alexander the Great -

Some of the most notable looters were other emperors! It's said that the Roman emperor Caligula took Alexander's breastplate, and the Egyptian king Ptolemy IX had the coffin melted down to be made into coins. His remains have been missing since 200 CE, and theories about his location stretch from Australia to Venice.

© Getty Images

Glenn Miller -

Glenn Miller was a best-selling musician in the 1930s and 1940s, and has been called one of the greatest big-band leaders of all time. He joined the Airforce in World War II, where his musical skills came in handy! In 1944, he began a journey to France so his band could play for the troops in Paris.

© Getty Images

Glenn Miller -

However, his plane never reached its destination. Miller, his two companions, and his plane disappeared somewhere over the English Channel and were never seen again.

© Getty Images 

Vlad the Impaler - Vlad III, more commonly known as Vlad the Impaler, was a notoriously cruel leader and the inspiration for Bram Stoker's 'Dracula.' His vicious methods of disposing with his enemies earned him his blood-thirsty reputation.

© Public Domain

Vlad the Impaler -

He is known to have had the bodies of his victims impaled on spikes for display, sometimes while they were still alive. When Vlad was finally killed by the Ottomans, it's said that his head was put on a spike as proof that he was dead. But the final resting place of his body remains unknown.

© Public Domain 

Genghis Khan -

Genghis Khan was another tyrant ruler, but unlike Vlad, he disappeared at his own request. He was in his sixties when he died, and it's believed he succumbed to long-term injuries he got when he fell off a horse.

© Getty Images 

Genghis Khan -

On his deathbed, he insisted that he be buried secretly in an unmarked grave. After the slaves buried his body, they were killed. Then, the soldiers who killed the slaves were also killed. His system must have worked, as no one has been able to locate his remains to this day.

© Getty Images 

Anthony and Cleopatra -

Cleopatra was the last and most notorious ruler of Egypt, and Mark Anthony was her famous lover. As their empire was falling to the Roman Emperor Octavian, the couple resolved to kill themselves. Mark Anthony stabbed himself with a sword, thinking Cleopatra was already dead.

© NL Beeld

Anthony and Cleopatra -

Cleopatra was captured but managed to kill herself by having a poisonous snake bite her. Historians say that Octavian allowed Cleopatra and Mark Anthony to be buried together, but the location is unknown. Their bodies may be lost in the sands of Egypt.

© Getty Images 

Harold Holt - Harold Holt was made Prime Minister of Australia in 1966. He served for two years, but tragically disappeared one day in 1967. He went for a swim at his favorite spot on the beach and never returned.

© Getty Images

Harold Holt - His clothes were found on the sand where he left them, but no other trace of him was ever recovered. He was a strong swimmer, but it's speculated that he was either pulled out to sea or killed by a shark. An expression was coined after his death. To "do a Harry Holt" means to abruptly disappear.

© Getty Images

Oscar Zeta Acosta -

Oscar Zeta Acosta was a controversial Mexican-American writer and activist. He was perhaps best known for his friendship with writer Hunter S. Thompson, who portrayed him as the character Dr. Gonzo in his famous book 'Fear and Loathing in Las Vegas.' He was played by Benicio del Toro in the 1998 film adaption starring Johnny Depp.

© BrunoPress

Oscar Zeta Acosta -

As you might guess if you've seen the movie, Acosta had a proclivity for recreational activities. While traveling in Mexico, Acosta called his son to say he was hitching a ride on a boat that was "full of white snow." He was never seen or heard from again. It's speculated that he may have gotten on the wrong side of some dealers, suffered an overdose, or was assassinated for political reasons.

© Getty Images

Davy Crockett -

Davy Crockett was a famous American frontiersman and has been a popular folk hero for centuries. It's known that he died defending the Alamo in the famous siege that took place during the Texas Revolution. What we don't know is how exactly he died or where he ended up.

© Getty Images 

Davy Crockett -

Those who died at the Alamo were burned to ashes by the Mexican army. There's a marble box at the Cathedral of San Fernando that is said to contain the ashes of Crockett and several other frontier heroes, but historians find it unlikely the ashes really belong to Crockett.

© Getty Images

Solomon Northup -

Solomon Northup was a free African-American man who was kidnapped and sold into slavery. He finally regained his freedom and wrote the incredible memoir 'Twelve Years a Slave,' which was turned into an Oscar-winning movie in 2013.

© Getty Images 

Solomon Northup -

Unfortunately this was not the happy ending of his story. He became a traveling lecturer and disappeared in 1857 during a trip to Canada. Some believe that he was again kidnapped and sold into slavery, or killed for his abolitionist ideals.

© NL Beeld

Jean Spangler -

Jean Spangler was an model, dancer, and actress during the Golden Age of Hollywood. One day she left her house telling her family she was going to meet her ex-husband to discuss child support and then had a night-shoot for a movie. She never returned home, and it turned out that her ex-husband had no plans to meet her and there was no filming scheduled for that night.

© Getty Images

Jean Spangler -

It seemed like maybe she had planned to disappear, but two days later her purse was found near a park with the straps broken as if someone had torn it off her shoulder. More than 160 people searched the area but found no further traces of her. Her case remains open to this day, although it's assumed she died when she disappeared in 1949 at the age of 26.

© Getty Images 

Amelia Earhart - Amelia Earhart may be the most famous missing person in the world. She was the first female aviator to fly solo across the Atlantic Ocean. In 1937, she and her navigator set off an a highly publicized flight around the world. They made it 22,000 miles (35,405 km) of the 29,000- mile (46,670 km) journey when they ran into trouble.

© Public Domain

Amelia Earhart -

Earhart radioed for help while flying over the Pacific Ocean, indicating that they were dangerously low on fuel. Rescue attempts were made, but communication ceased and the plane was never located. Extensive searches at the time and in the subsequent century failed to uncover her whereabouts.

© Getty Images

Amelia Earhart -

Her disappearance has consumed historians, scientists, conspiracy theorists, and the regular American alike. Recently, forensic scientists began to believe they have confirmation that her bones were found. Does this mean we finally get closure?

Sources: (Mental Floss) (TV Over Mind)

See also: Missing people who were found alive

© Getty Images