El Gordo (lit. The Fat One) (ACT-CL J0102-4915 or SPT-CL J0102-4915) is the largest distant galaxy cluster seen as of 2011.
It has (2014) the record for being the largest distant galaxy cluster we have discovered. Its mass is slightly less than three quadrillion solar masses[1][2][3][4] Later its mass was reduced to about 2.1 quadrillion solar masses with a 10% uncertainty.
It was found by NASA's Chandra X-ray Observatory, the Atacama Cosmology Telescope (funded by the National Science Foundation) and the European Southern Observatory's Very Large Telescope.[5]