CAMBRIDGE (Reuters) - Mark Zuckerberg returned to Harvard officially for the first time, winning a warm welcome from the university where he created Facebook and embarked on a well-chronicled meteoric ascent. It was clear Zuckerberg was no longer the dropout who left the iconic Ivy League institution, even if he still dresses in the classic campus uniform of T-shirt, jeans and sneakers. If he werent so famous, the billionaire portrayed as the flawed protagonist of the Oscar-nominated The Social Network could have passed for any one of the hundreds of computer science students.