David "Dai" Greene (born 11 April 1986) is a Welsh retired hurdler who specialised in the 400 metres hurdles, competing internationally for both Wales and Great Britain, as well as Europe in the IAAF Intercontinental Cup.

In a 'golden' sixteen-month period between 2010 and 2011, Greene dominated his event at international level, winning every international title available in that period: he won the World, European, Diamond League and (for Wales) the Commonwealth Games titles in quick succession, in addition to winning the event as part of both the European Team Championships for Great Britain and the IAAF Continental Cup for Europe.

He beat Frenchman Fadil Bellaabouss by a narrow margin to mark an impressive return, following an ankle injury which had ruled him out for six weeks of the season.

On 31 July 2010, he won the Gold Medal in the 400m hurdles at the European Athletics Championships in Barcelona, with fellow Welshman Rhys Williams getting the silver.

[13] On 1 September 2011, at the World Athletics Championships in Daegu, South Korea, Greene won the gold medal, overtaking a strong field in the final straight.

[14] At the Diamond League event in Paris on 6 July 2012, Greene ran a personal best of 47.84 secs in finishing second to Javier Culson to move even closer to the British record in the 400m hurdles.

[16] In the final Greene finished fourth behind 2004 Olympic champion Félix Sánchez, surprise American Michael Tinsley and Javier Culson, running slower than he had in the semi-final.

Greene resultantly withdrew himself from consideration for the 2014 European Athletics Championships, because of lack of form and a failure to make the agreed qualification time.