Social media has been flooded with touching tributes in honor of boxing legend Muhammad Ali, who died Friday evening at the age of 74. Many people, including Ali’s celebrity friends, have taken to Twitter and Instagram to share their condolences over his death.

As previously reported, Ali died at the Scottsdale Osborn Medical Center in Arizona. The athlete, known to many as “the Greatest,” was admitted to the hospital Thursday due to respiratory problems. Bob Gunnel, a spokesman for the Ali family, told MSNBC in a statement  the boxer was surrounded by his family at the time of his death.

“It was a very peaceful passing, and they are with him as we speak,” he said. “You know, we lost a great person in this world tonight.” Gunnel also said there is not an official reported cause of death yet, but the family believes it “has to be from complications of Parkinson’s.” Ali had been battling Parkinson’s disease for over 30 years. Funeral arrangements for Ali, born Cassius Marcellus Clay Jr., are still being made but will take place in his hometown of Louisville, Kentucky.

Shortly after the family confirmed Ali’s death, one of his daughters, Rasheda Ali, took to Twitter to share a message about her father. “The Greatest Man that ever lived,” she tweeted. “Daddy my best friend & my Hero You R no longer suffering & now in a better place.” Another daughter, Hana Ali, shared a photo of her and her father, writing: “Our father was a ‘Humble Mountain!’ And now he has gone home to God. Pray for the peace of this beautiful soul and for the happiness of his further journey. God bless you daddy. YOU ARE THE LOVE OF MY LIFE!”

Many celebrities also posted on social media about the death of Ali. Jennifer Lopez posted a photo of the athlete on Instagram, writing that Ali always inspired her and others to “want to be their greatest!” She added, “#RIP #ALI #inspiration #suchalegend.” Viola Davis also shared a sweet message about Ali, tweeting: “Muhammad Ali. You were the greatest. Thanks for giving me strength and a love of self when I couldn’t muster it. RIP.” Madonna was clearly stunned by the news and took to Instagram to share a photo of her and Ali. “What is going on??!! We are losing all of our National Treasures,” she wrote, referencing the deaths of Prince and David Bowie. “Our Pillars of Humanity. He was the Greatest!”

Lopez, Davis and Madonna are far from the only celebrities reacting to the death of Ali. See more of their moving tweets below.