2012 shooting death of Trayvon Martin sparks a movement.

Black Lives Matter was created in 2012 after George Zimmerman was acquitted in the shooting death of 17-year-old Trayvon Martin. The unarmed black teen was fatally shot by Zimmerman in February 2012, after walking through a gated Florida community wearing a hoodie and carrying a can of soda and a bag of candy. Zimmerman was acquitted of the killing, citing Florida's stand your ground laws as a defence. 

Black Lives Matter Trayvon Martin George Zimmerman

Americans angry at the acquittal of George Zimmerman in the shooting death of Trayvon Martin protest in Los Angeles in July 2013. (Robyn Beck/AFP/Getty)

Black Lives Matter George Zimmerman Trayvon Martin

George Zimmerman wipes his brow before the state's closing arguments during his trial in July 2013. He was acquitted of second-degree murder. (Gary W. Green/Reuters )

How #BlackLivesMatter became a worldwide rallying cry

After Zimmerman's acquittal, three young, black, female activists — Alicia Garza, Patrisse Cullors and Opal Tometi — founded the Black Lives Matter movement. According to the organization's website, "Black Lives Matter affirms the lives of black queer and trans folks, disabled folks, black undocumented folks, folks with records, women and all black lives along the gender spectrum."

The group has no formal structure, but organizes protests over the deaths of black people at the hands of police and issues such as racial profiling, police brutality, and racial inequality in the U.S. justice system.

Black Lives Matter Alicia Garza Patrisse Cullors Opal Tometi

From left, Alicia Garza, Patrisse Cullors and Opal Tometi, the three women who created the Black Lives Matters movement, attend a New York Women's Foundation 'Celebrating Women' breakfast on May 14, 2015. (Jemal Countess/Getty)

Black Lives Matter Trayvon Martin

Supporters gather during a candlelight vigil at a memorial set up for Trayvon Martin outside the community where he was killed in 2012. (Mario Tama/Getty)

Black Lives Matter Trayvon Martin George Zimmerman

Hundreds of protesters participated in rallies across the country to express anger over the 2013 acquittal of George Zimmerman, who fatally shot Trayvon Martin. (David McNew/Reuters )

Police killing of Michael Brown galvanizes movement, triggers unrest in Ferguson, Mo. 

More than a year after Zimmerman was acquitted, Michael Brown, another unarmed black teenager, was shot dead by a white police officer in Ferguson, Mo., in August 2014. A grand jury declined to indict Darren Wilson, the officer who killed the 18-year-old, triggering widespread protests in the St. Louis suburb. 

Black Lives Matter Ferguson Michael Brown

A demonstrator argues with police officers during a protest after a grand jury failed to indict Ferguson police officer Darren Wilson in the shooting death of Michael Brown, in December 2014. (Jim Young/Reuters )

Black Lives Matter Ferguson Michael Brown

Demonstrators stage a die in to mark the one-year anniversary of the shooting death of Michael Brown in Ferguson, Aug. 9. (Scott Olson/Getty )

Black Lives Matter Ferguson Michael Brown

A man is doused with milk and sprayed with mist after being hit by an eye irritant from security forces trying to disperse protesters in Ferguson in August 2014. (Adrees Latif/Reuters )

Protests spread as more black lives lost.

The deaths of Eric Garner, Freddie Gray and Sandra Bland sparked more protests across the United States. Garner, a 43-year-old father of six, was killed after being put in a choke hold by an NYPD officer in July 2014. Garner was stopped by police for selling loose cigarettes and the officer involved in the incident was cleared by a grand jury. The hashtags #HandsUpDontShoot and #ICantBreathe galvanized support online from around the world.

Black Lives Matter Eric Garner

A protester does the don't shoot pose at a demonstration following a Staten Island grand jury's decision not to indict police officer Daniel Pantaleo on the July 2014 chokehold death of Eric Garner. (Andrew Kelly/Reuters )

Freddie Gray died April 19 of a severe spinal injury he suffered while in police custody. Six Baltimore police officers were charged in Gray's death. Jury selection in the trial of one of the officers began on Monday.

Black Lives Matter Freddie Gray

The death of Freddie Gray, who suffered a critical neck injury in the back of a police van in Baltimore in April 2015, stoked new anger over police treatment of minorities and added fuel to the Black Lives Matter movement. (Sait Serkan Gurbuz/Reuters)

Sandra Bland was found dead in a Texas jail cell on July 13, three days after she was arrested during a traffic stop. The 28-year old was stopped by police for failing to signal a lane change. The conduct of the officer involved has been criticized, sparking the hashtag #BlackWomenMatter.

Black Lives Matter Sandra Bland

A protester demonstrates outside the funeral for Sandra Bland in the Chicago suburb of Lisle on July 25, 2015. (Jim Young/Reuters )

Video of Laquan McDonald death costs Chicago police superintendent his job.

Chicago Mayor Rahm Emanuel fired police Supt. Garry McCarthy on Dec. 1, 2015, following days of protests over the death of 17-year-old Laquan McDonald. The black teenager died after he was shot 16 times by a white police officer in October 2014. Chicago police refused to release the video of the killing for more than a year. 

Killings Police Chicago Laquan McDonald Black Lives Matter

Chicagao Mayor Rahm Emanuel, left, looks on as Chicago police Supt. Garry McCarthy announces a murder charge against police officer Jason Van Dyke in the October 2014 death of Laquan McDonald. McCarthy was fired Dec. 1, 2015, over his handling of the case after a video of the shooting became public. (Charles Rex/AP)

And the movement rolls on.

Protests associated with the Black Lives Matter movement continue in the wake of McDonald's death and the initial refusal of Chicago police to release video of the deadly encounter.

CHICAGO Laquan McDonald Black Lives Matter

Protester Lamon Reccord, 16, confronts police during a Black Lives Matter demonstration in Chicago on Nov. 25. (Andrew Nelles/Reuters)