Monday marked Martin Luther King Jr Day – a public holiday in the US to remember the world famous activist and his “fight for justice”.
Dr King, who was one of the most prominent leaders in the civil rights movement from 1955 onwards, was assassinated in Memphis, Tennessee, in 1968.
He was well known for his “I have a dream” speech, and won the Nobel Peace Prize in 1964.
Obama praised Dr King’s work, encouraging others to engage in community efforts to honour his legacy.
“Reverend Dr. Martin Luther King Jr.’s fight for justice took patience and perseverance, leadership and compassion, and a love for humanity that all of us should strive for,” she wrote in a series of posts.
Oscar-winning actresses Jennifer Hudson and Halle Berry, and Will and Jaden Smith were also among those to post online tributes to the minister.
Sharing a picture of herself on the set of 2021 Aretha Franklin biopic Respect, Hudson said: “When it comes to a giant like Martin Luther King Jr., words never seem enough to capture the magnitude of his legacy.
“A couple years ago, while filming Respect, I got to sit on the steps of Dr. King’s birth home. I sat there soaking in the significance of that place, and I imagined him sitting on these very steps as a child, unaware of the impact he would have.
“As we honor him today, let’s continue his dream, raising up more Dr. Kings that make this world a better place to live.”
Berry wrote: “Today we honour the work of Reverend Dr Martin Luther King Jr and all those that worked towards a better future for ALL people.
Smith and his son also both posted pictures in tribute to Dr King.