There were many times during Martin Luther King Jr.'s life that he showed great leadership.

There's a specific day, however -- and a single speech, really -- during which he dramatically grabbed hold of that kind of leadership role for the first time.

While King's most famous speech is likely his "I Have a Dream" speech in Washington in August 1963, the moment I'm thinking off was almost eight years earlier.

King was just 26, unknown, and literally had only 15 minutes to prepare. Here's the story.

'Hadn't been there long enough'

King would be 91 if he were alive today, but he was only 39 when he died. So, his civil rights story is really a young man's story throughout.

He grew up in Atlanta, graduated from Morehouse College at 19, then earned a bachelor of divinity at 22, and moved to Montgomery, Alabama while still finishing his doctorate in theology in 1954.

Thus, King had only been pastor of Dexter Avenue Baptist Church in Montgomery for a year, and harbored "no ambition to become the leader of a movement," in the words of Louis Menard, when Rosa Parks, 42, was arrested for refusing to give up her seat on a Montgomery city bus to a white passenger.

Over the next few days, as support for a boycott of the Montgomery busses brewed, King was elected president of the group that formed to organize it. 

"The advantage of having Dr. King as president," Parks later said, "was that he was so new to Montgomery and to civil rights work that he hadn't been there long enough to make any strong friends or enemies."

5,000 people and no notes

I've tried to reacquaint myself with the history of this moment as part of  writing this article. Menand's 2018 article in The New Yorker is a great source.

Menard recounts how King was became president of the brand-new Montgomery Improvement Association at 6 p.m., and then had to give a speech as its new leader in front of a huge crowd at 7.

King rushed home to tell his wife, realizing he was left with only 20 minute to write his speech, and wrote later that he lost five minutes having a panic attack. 

Five thousand people turned out at the church. King's speech wasn't filmed, but his wife, Coretta Scott King, thought to record an audio version, which you can hear in the YouTube video below. 

It's worth listening to, remembering that it's basically King's first pubic civil rights speech. (It also lasts almost exactly 15 minutes.)

Already, he's structuring his speech with calls-and-responses, and speaking with poetry. If you're pressed for time, fast forward to about 4:36.

'Found his calling'

The bus boycott ran for 381 days, crippling the city bus system's finances.

Black people walked, or took black-owned cabs (which lowered their rates to match the bus fares). Later, when the city cracked down on taxi drivers, they organized carpools. 

But there was violence: King's house was firebombed two months after his speech. Some black citizens boycotting the busses were physically attacked. 

Ultimately the city indicted the carpool drivers (and King) for interfering with the bus system. (King spent two weeks in jail.)

Eventually the busses were desegregated, but more because of an accompanying lawsuit; the U.S. Supreme Court ruled in November 1956 that that bus segregation is unconstitutional. Of course this was just the beginning as far as King and the civil rights movement were concerned.

But that evening, that speech, and those 15 minutes set the course of the remainder of King's life.

As Menard wrote: "King inspired not just his listeners that day. He inspired himself. He must have realized, when he stepped down from the pulpit, that he had found his calling."