US President Barack Obama and Microsoft's Bill Gates are among those honouring "insanely great" Apple co-founder Steve Jobs, who has died aged 56.
The legendary former chief executive of the world's largest technology firm passed away after a long battle with pancreatic cancer.
As tributes to Mr Jobs flooded in, Mr Obama described him as "a visionary".
"Steve was among the greatest of American innovators - brave enough to think differently, bold enough to believe he could change the world, and talented enough to do it," he said in a statement.
"The world has lost a visionary. And there may be no greater tribute to Steve's success than the fact that much of the world learned of his passing on a device he invented."
Microsoft Corp co-founder and chairman Bill Gates had been a longstanding friend and competitor of Mr Jobs.
He used one of the Apple icon's favourite expressions - "insanely great" - in his tribute.
"For those of us lucky enough to get to work with him, it's been an insanely great honour," Mr Gates said in a statement.
"I will miss Steve immensely. The world rarely sees someone who has had the profound impact Steve has had, the effects of which will be felt for many generations to come.
"Steve and I first met nearly 30 years ago, and have been colleagues, competitors and friends over the course of more than half our lives.
"I'm truly saddened to learn of (his) death."
Facebook chief executive Mark Zuckerberg wrote on his Facebook page: "Steve, thank you for being a mentor and a friend.
"Thanks for showing that what you build can change the world. I will miss you."
Former Yahoo boss Carol Bartz, who had known Mr Jobs for about 30 years, said: "It's the ultimate sadness. First of all, it's a young person who was revered, sometimes feared, but always revered.
"He was a very special person, and he didn't get to where he was by having people like him all the time.
"He got to where he was because he had a vision and a purpose. It's easy to try and please everyone, but he kept to his principles."
Google chief executive Larry Page said on his Google+ account: "Am very, very sad to hear about Steve.
"He was a great man with incredible achievements and amazing brilliance."