On Monday, the United States celebrates the life and legacy of civil rights activist Martin Luther King Jr, who would have turned 89 years old.

Beginning in 1971, three years after he was assassinated in Memphis, Tennessee, many US cities and states began to mark what is now known as "MLK Day".

More than 30 years later, the day is still traditionally celebrated as one of service, honouring King's legacy and words, including his famous "I have a dream" speech, which continue to resonate today.

Here is a list of some of King's most emblematic quotes:

On injustice

In a letter from the Birmingham city jail in 1963, King wrote:

"Injustice anywhere is a threat to justice everywhere."

We are caught in an inescapable network of mutuality, tied in a single garment of destiny. Whatever affects one directly, affects all indirectly."

Injustice anywhere is a threat to justice everywhere. Martin Luther King Jr

On truth and love

In 1964, King received the Nobel Peace Prize for his non-violent fight against racial inequality. The Baptist minister, Nobel Laureate and civil rights activist dedicated his life to "work for peace, social justice, and opportunity for all Americans".

In his acceptance speech he said:

"I refuse to accept the cynical notion that nation after nation must spiral down a militaristic stairway into the hell of thermonuclear destruction, "

"I believe that unarmed truth and unconditional love will have the final word in reality," he continued.

"This is why right temporarily defeated is stronger than evil triumphant. I believe that even amid today's mortar bursts and whining bullets, there is still hope for a brighter tomorrow."

I believe that unarmed truth and unconditional love will have the final word in reality. Martin Luther King Jr

The legacy of Coretta Scott King, the woman who stood by Martin Luther King Jr. pic.twitter.com/7GRaJOKyUJ — AJ+ (@ajplus) January 17, 2018

On education

In 1947, King wrote for the Morehouse College Student Paper, The Maroon:

"To save man from the morass of propaganda, in my opinion, is one of the chief aims of education. Education must enable one to sift and weigh evidence, to discern the true from the false, the real from the unreal, and the facts from the fiction,"

"Intelligence plus character - that is the goal of true education,".

"If we are not careful, our colleges will produce a group of close-minded, unscientific, illogical propagandists, consumed with immoral acts. Be careful, brethren! Be careful, teachers!"

Intelligence plus character - that is the goal of true education. Martin Luther King Jr

On racism and violence

As reported by the Chronicle in 2008, in 1957 King delivered a speech in Finney Chapel in which he said:

"The non-violent Negro is seeking to create the beloved community. He directs his attack on the forces of evil rather than on individuals,"

"The tensions are not between the races, but between the forces of justice and injustice; between the forces of light and darkness."

The tensions are not between the races, but between the forces of justice and injustice. Martin Luther King Jr

5. On religion

King was the author of the book Strength To Love, a collection of sermons that he wrote on a number of topics, including religion.

In one of King's sermons, he extolled the need for a "tough mind". "The modern world", he said, has far too much "softmindedness" of "unbelievable gullibility".

King also had great appreciation and respect for science.

"There may be a conflict between softminded religionists and toughminded scientists. But not between science and religion.

"Their respective worlds are different and their methods are dissimilar.

"Science investigates; religion interprets. Science gives man knowledge which is power; religion gives man wisdom which is control. Science deals mainly with facts; religion deals mainly with values. The two are not rivals. They are complementary."

Science gives man knowledge ... religion gives man wisdom Martin Luther King Jr

In celebration of Dr. Martin Luther King Jr Day. pic.twitter.com/7tYmAXiS7P — Eric Thomas (@Ericthomasbtc) January 15, 2018

On peace

"True peace is not merely the absence of tension: it is the presence of justice," Martin Luther King responded after being accused of disturbing the peace during the "bus boycott" in Montgomery, Alabama.

The bus boycott was a 13-month political and social protest against the policy of racial segregation on public transit.

It ended on December 20, 1956. The US Supreme Court ultimately ruled that segregation on public buses is unconstitutional.