Fred and George Weasley were mischievous twin wizards born on 1 April, 1978 to Arthur Weasley and Molly Weasley (née Prewett). Although Fred was the oldest the two were both brilliant pranksters that co-founded and ran the joke shop Weasleys' Wizard Wheezes and were members of both Dumbledore's Army and the Order of the Phoenix.
See their individual articles for more information:
Behind the scenes
The actors who portrayed Fred and George are James and Oliver Phelps respectively. Oliver is actually the older twin, but Fred is older than George. Two differences between the Phelps twins is that Oliver has a mole on the right side of his neck, while James does not and James has a slightly deeper voice than Oliver.