Ukrainian film director Oleh Sentsov has been on a hunger strike in a Russian prison since May 14, demanding the release of dozens of Ukrainian political prisoners.

The outspoken opponent of Russia's seizure of Ukraine's Crimean Peninsula is serving a 20-year sentence on a conviction for planning terrorist acts. He denies the charges and has the backing of much of the world community.

Sentsov's hunger strike, taking place as the globe's attention is fixated on the World Cup being hosted by Russia, marks one of the highest-profile efforts to employ the tactic to put a spotlight on a political cause.

In the arsenal of the activist, the hunger strike stands out. That's because a hunger strike does harm directly to the protester and not the intended target. The protester relies on the moral force of their action, or the generated publicity, to achieve something.

Here are some of the more notable examples:

Mahatma Gandhi is considered the modern-day pioneer of civil disobedience and arguably the most famous hunger striker in history. During his lifetime, Gandhi went on several hunger strikes and fasts to protest against British rule in India. In total, Gandhi is said to have undertaken 17 fasts during India's independence movement with the longest such protest lasting 21 days.

For many in the West, the name Irom Sharmila won't ring any bells. But Sharmila held a hunger strike for 16 years in India, arguably the longest such fast in the world. Sharmila had been protesting a law giving the military sweeping search and detention powers.

For over a decade, the government force fed her by nasal drip, a common practice to keep hunger strikers alive. Sharmila ended her hunger strike in August 2016 with a lick of some honey that was spooned onto her palm.

Bobby Sands' deadly hunger strike is among the most recognized. He was one of 10 Irish Republican Army (IRA) members to launch a hunger strike in October 1980 in Northern Ireland's Maze prison to demand being treated as "special category" political prisoners, rather than criminals. Sands died on May 5, 1981, after 66 days on hunger strike. He was the first of 10 to die during the hunger strike, which was abandoned on October 3, 1981.

In the United States, Cesar Chavez is one of the few and probably most famous hunger strikers. Chavez was a Mexican-American union leader who fought for higher wages for farm workers. He staged several fasts, the first of which was for 25 days in 1968. He ended that fast by eating a piece of bread during a meeting with Senator Robert F. Kennedy, who at the time had a seat on the Subcommittee on Migratory Labor.

Chavez is not the only American to stop taking food to protest for a cause. Mia Farrow went on a hunger strike in 2009 to express solidarity with the people of the war-hit Darfur region of Sudan. The U.S. actress and activist fasted for 12 days over the Sudanese government's decision to expel foreign aid agencies. The then-64-year-old Farrow ended her protest fast on May 9 because of "health concerns."

In January 2012, more than 1,000 convicts at a prison in Kyrgyzstan went on hunger strike to protest living conditions in the Central Asian state's penitentiaries. However, the inmates at the prison in Bishkek added a gruesome twist, stitching their mouths shut. The protest lasted four days.

The 1989 student protests in Beijing's Tiananmen Square are largely remembered today for the iconic image of a lone man staring down a row of tanks in the square of the Chinese capital. However, hundreds of protesting students also vowed at one point to starve to death unless the government promised immediate democratic reforms. The hunger strike lasted one week.

Back in Ukraine, before Sentsov, arguably the most famous hunger striker was Nadia Savchenko. The former Ukrainian military helicopter navigator was imprisoned for two years in Russia on charges relating to the deaths of two Russian journalists in eastern Ukraine. Savchenko went on hunger strike twice, once for 83 days, during her incarceration from 2014 to 2016.

While next to impossible to verify, Ukraine is also the source of possibly the most bizarre hunger strike ever. Kyiv claimed dolphins trained by the country's military and seized by Russian troops died after "going on a hunger strike." The "dolphin army" was seized by Russian forces from the Crimean Military Dolphin Center during the seizure of the Ukrainian peninsula by Russian forces in March 2014.

The Ukrainian government's representative in Crimea, Boris Babin, claimed that the dolphins "refused not only to interact with the new Russian coaches, but refused food and died some time later."