Why is a Big Mac called 巨无霸 (jùwúbà)?
https://baike.baidu.com/item/%E5%B7%A8%E6%97%A0%E9%9C%B8/1226195

巨无霸 (巨毋霸) was a historical character who was famous for being a giant. Later people commonly use '巨无霸' as a nickname for something that is 'giant size'. For example, compare to modern dragonfly's modest 1-4 inches length, the dragonfly- like Meganeuropsis was no doubt a 'giant'(巨无霸) with it's 18 inches long body

Meganeuropsis- 青蜓中的巨无霸 (giant among dragonflies)



巨无霸 is not a translation of 'Big Mac', it is a Chinese name for 'Big Mac' . Someone gave 'Big Mac' this Chinese name because the selling point of 'Big Mac' is "it is BIG" 

'Big Mac' is 'giant' among hamburgers