The respected politician has been hailed as 'a true son of Sandwell' by friend Tom Watson, the deputy leader of the Labour Party and West Bromwich East MP.
Labour leader Jeremy Corbyn also paid tribute to Mr Cooper, saying: "Darren's contribution to Sandwell and the Black Country is immeasurable.
"A Councillor for nearly twenty five years and leader of Sandwell Council since 2009, he was one of the most important Labour Leaders in Britain.
"He was a huge talent – he fought for Labour values to get the best for the people that he served so diligently in Sandwell.
"Our movement is diminished by his loss and his experience, charisma and leadership will be sorely missed. My deepest sympathies go to his family at this extremely sad time."
Former prime ministers Tony Blair and Gordon Brown were among the many people paying tribute to the popular Labour politician, described as Mr Sandwell.
Councillor Cooper was elected in the Soho and Victoria ward in Smethwick - where he grew up - in 1991 and became leader of the authority in December 2009.
The married father-of-three, who died at home on Saturday night, had been widely touted as a possible candidate for the new metro mayor of the West Midlands Combined Authority, which he played a leading hand in bringing together.
Mr Watson said: "There will be many members of the Labour Party who will wish to pay their tributes to Darren as a civic and political leader.
"I would like to remember the funny and humorous friend who loved the Albion and bank holiday fishing.
Councillor Cooper's daughter Holly Jordan Cooper posted a moving tribute on Facebook.
She wrote: "I actually can't believe I am writing this, but last night I lost the most influential man in my life, he taught me so much and words can't describe how I feel at the moment, I can't believe I have to go on the rest of my life without my father, he meant so much to everyone and was such a special person.
"Nan please greet him with open arms and take care of him. Dad I know you will always be with us in whatever we do, I love you so much!"
The outpouring of grief on Twitter saw Councillor Cooper's name become the seventh highest trend nationally yesterday afternoon.
Council deputy leader Councillor Steve Eling said the death was a terrible shock to all those who knew Councillor Cooper.
Mr Eling will assume the role of council leader, as is procedure.
Councillor Cooper, who was born in 1963, grew up on a a council estate in Windmill Lane, Smethwick and attended Crocketts Lane Primary and Smethwick Hall Boys secondary. He spent three decades working as a mental health nurse.
His love for West Bromwich Albion was well known, and he was a familiar face at The Hawthorns, while he was also a keen angler.
Councillor Cooper was chairman of the West Midlands Police and Crime Panel and a member of the region's Integrated Transport Authority. Mike Bird, a Conservative who leads neighbouring Walsall Council, said: "We have lost a great ally, a great Black Country politician and I've lost a bloody good friend.
"Darren was a tremendous asset to the West Midlands and you can't replace a bloke like that.
"Darren always led from the front and he was Mr Sandwell – when you thought of Sandwell you thought of Darren, and vice versa."
Tony Blair last night said: "Darren Cooper was one of Labour's most committed and passionate local government leaders of the last 20 years and stood resolute in his support for the people of Sandwell. A long-serving councillor, he worked diligently to implement Labour's core values of social justice and equality of opportunity despite the huge challenges faced by local government over the last few years.
"My deepest sympathies are with Darren's family, friends and colleagues at this very difficult time."
Mr Brown said: "Like many I am shocked at the sudden death of Councillor Darren Cooper.
"He had an outstanding record of public service which was recognised across the country and his work for the people of Sandwell will be sorely missed."
Former Labour Party leader Ed Miliband, added: "I am deeply shocked to hear that Darren Cooper has died. He was a great leader of his council and one of the most decent people in our movement.
"He was charismatic, innovative, in touch with the people he represented and a deeply loyal person.
"His death at such an early age is a terrible tragedy most of all for his family and friends and for the whole Labour Party."
Councillor John Clancy, Leader of Birmingham City Council, said: "I was heartbroken to hear this morning about Darren's passing away. I deeply valued his personal friendship and his steadfast personal support over many years. He was someone who I could go to for advice about anything and he'd give it with wisdom, humour and realism.
"I have lost a great friend. Sandwell has lost one its great sons, and Birmingham has lost one of its great allies. We all feel lost today. The political and economic life of the West Midlands are also much the poorer for his passing. My thoughts and prayers are with Karen and the family: my heart goes out to them this Easter.
"On behalf of Birmingham City Council and the citizens of Birmingham we extend our deepest sympathies to Darren's family and the people of Sandwell."
Adrian Bailey, MP for West Bromwich West, said: "I am shocked and deeply saddened by this news. I have known Darren for over 25 years, as a friend, council colleague and latterly, council leader.
"He had a passion for public service and demonstrated great skill as a politician. He has navigated Sandwell Council through a very difficult period, managing enforced economies but ensuring that they were fairly implemented and commanded public support. Labour's strength on Sandwell Council is a reflection of his qualities as leader. I am sure he would have gone on to serve in even higher positions.
"He will be greatly missed as a warm, caring individual who could have achieved even more for the Black Country community he loved.
"My heartfelt condolences go to his family at what must be an incredibly difficult time for them."
John Spellar, MP for Warley, said: "He was a good friend and a stalwart of the Labour Party. He had not only made a big contribution as Leader of Sandwell but was starting to be a major figure in local government nationally. It is shocking that he has died so young."
Ian Austin, MP for Dudley North, said: "This is really dreadful news. It has come as a terrible shock and I feel so sorry for his family.
"He was a great public servant for the area in which he was born, grew up and loved so much, and for the wider West Midlands as well, and he did very important work in the Labour Party.
"He was great to work with, but was a great friend and a very nice guy too, giving me very valuable advice and real support - both as a Black Country MP and when I was regional minister. We're all really going to miss him very much."
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