The legendary star passed away on his 79th birthday after suffering complications from pneumonia.
His death has rocked the country world and many of Haggard's friends, fans and collaborators have taken to social media to mourn his loss.
Dierks Bentley was among the first to comment on the sad news, writing, "literally just fell to the floor. can't believe we lost the hag. rip Merle Haggard", while Brad Paisley wasn't far behind, commenting, "There are no words to describe the loss & sorrow felt within all of music with the passing of Merle Haggard. Thank God for his life & songs."
Carrie Underwood posted, "Love and prayers for the Haggard family. Merle was a pioneer...a true entertainer...a legend. There will never be another like him," and Sheryl Crow tweeted, "The world will not be the same without @merlehaggard in it. Voice of reason, good man, true American artist. An original. RIP #MerleHaggard".
"Country music has suffered one of the greatest losses it will ever experience," wrote Charlie Daniels. "Rest in peace Merle Haggard."
Jason Aldean shared a photo of himself with the late legend and captioned it, "extremely sad to hear of the passing of one of the greatest of all time Mr. Merle Haggard today. so glad i had the chance to meet him. You will forever be missed and remembered."
Kings of Leon rocker Nathan Followill remembered Haggard as "truly one of my all time favorites", while Lady Antebellum's Hillary Scott branded him a "cornerstone of country music", and LeAnn Rimes added, "We lost a bad a** man, a great poet! I love you Merle. Prayers for his family. R.I.P. #MerleHaggard".
Fellow singers Jake Owen, Dustin Lynch, Billy Currington, and Chely Wright have also offered up their condolences to Haggard's family online, while Jackass prankster Johnny Knoxville lamented, "We've lost an American original. RIP Merle Haggard. Today was his birthday too."