How many times has a person been elected president and not received the majority of the popular vote?

Kevin Rudd

It has happened 3 times:

1876: Rutherford B. Hayes won the electoral vote with 185/369 votes but lost the popular vote to Samuel Tilden.

1888: Benjamin Harrison won the electoral vote with 233/401 but lost the popular vote to Grover Cleveland.

2000: George W. Bush won the electoral vote with 270/538 but lost the popular vote to Al Gore by a very small margin.