Geoffrey Kiprono Mutai (born 7 October 1981) is a Kenyan long distance runner who specialises in road running competitions. On 18 April 2011 at the Boston Marathon, Mutai ran the fastest marathon ever at the time in a time of 2 hours 3 minutes 2 seconds (4:41 per mile pace / 2:54 per kilometer pace), though the time was not recognised by the International Association of Athletics Federations as a world record since the Boston course does not meet the criteria to be eligible for the mark.
His other significant victories include the Monaco Marathon. He is also a strong half marathon runner, with wins at the Valencia Half Marathon and RAK Half Marathon, and a best of 58 minutes 58 seconds, to his name. He also won the 2011 New York City Marathon with a time of 2 hours 5 minutes and 5 seconds (4:46 per mile pace), breaking the course record set by Tesfaye Jifar of Ethiopia in 2001, and repeated his performance at the 2013 New York City Marathon with a time of 2 hours 8 minutes and 24 seconds.