Facebook co-founder Mark Zuckerberg has announced he had become a father — and pledged to give away his fortune to make the world a "better place" for baby daughter Max and others.

In a letter to Max posted on his Facebook page, Zuckerberg and his wife said they were going to give away 99 per cent of their company shares — with an estimated value of $45 billion — in an effort to make a happy and healthy world for her and all children.

"Max, we love you and feel a great responsibility to leave the world a better place for you and all children. We wish you a life filled with the same love, hope and joy you give us. We can’t wait to see what you bring to this world," the letter said.