Lady Gaga and Jennifer Lopez celebrate Martin Luther King Jr. Day

Lady Gaga, Jennifer Lopez, and Mark Ruffalo are among the stars celebrating Martin Luther King Jr. Day by saluting the late civil rights icon online.

The bank holiday falls just four days before President-elect Donald Trump's inauguration and the timing didn't go unnoticed by many celebrities, some of whom called on followers to continue the fight for equal rights, unity and respect - the same issues Dr. King fought for - as the controversial Republican prepares to take office.

Gaga was among those who quoted a line from King's historic I Have A Dream speech in Washington, D.C. in 1963, tweeting: "With this faith, we will be able to work together, to pray together, to struggle together," while Lopez added another part of MLK's famous speech: "This is our hope, and this is the faith that I go back to the South with. #IHaveADream".

Dance star Moby took to Instagram to share the Dr. King quote, "The time is always right to do what is right", and captioned the post, "Our best national holiday: Martin Luther King Jr day. If we have a patron saint of America it is Dr. King. We need to follow his lead: rise up, take action, stay committed, stay involved. 'The moral arc of the universe is long but it bends towards justice'. #fightthegoodfight".

Meanwhile, Avengers actor Mark Ruffalo tweeted, "Now is the time to stand up and be inspired", and Ben Stiller wrote, "Respect. Now more than ever."

Oscar winner Octavia Spencer took to Instagram with her message and wrote: "Today I honor #DrKing because his dream is what my mom wanted for her children. I think they, Dr. King and my mom, are both standing up in their graves at the serious 180 this country is both committing and enduring; but YOU can change that.

"If 2016 taught us anything it's just how precious and limited our time on Earth is. Start living your dream... today... Just making any effort toward your dream will make you happy. And YOUR being happy means that you will then affect someone else. Live. Live YOUR dream!!! P.S. in these uncertain times you will need something to hold on to, something positive, something that's uniquely yours. Be the light for those around you!!! I promise I will be. And, really big and.... STOP engaging with the hate baiters. They only seek to dim your light!!!"

Other stars who honored King on social media included Alicia Keys, Pharrell Williams, Oprah Winfrey, and Kerry Washington.