When Michael Bloomberg became New York City's mayor 12 years ago, he was a political neophyte faced with the aftermath of the Sept. 11 terror attacks.

Now, as he prepares to leave office at month's end, he has dramatically reshaped the city.

New York has never been safer or cleaner and welcomes more than 50 million tourists a year.

But it also faces widening income inequality and strained relations between police and some minority communities.

Bloomberg's legacy will be debated, but his impact is clear. One pundit says it is "unlikely that there's going to be another Bloomberg."

His great fortune rewarded allies and silenced critics, allowing him to largely stay above partisan fights.

He vowed to never seek office again but will fund pet causes like gun control.