"Who are they?"; asks the burly leader of a pack of motorcycle savages. Before the dust settles and the last piston throbs, he'll especially know who one of them is. So will movie fans. Mel Gibson gave notice that he was a name to reckon with in the revved-up, trend-setting first of Gibson's Mad Max collaborations with filmmaker George Miller. Gibson portrays Max Rockansky, the fearless, leather-suited cop waging war with kill-crazy bikers who targeted his family. It is a war that must be seen to be believed, a road-scorching, neo-punk, take-no-prisoners combat set in a post-apocalyptic Australia. In the end, a lone man travels a ribbon of highway now free of the unroadworthy-a highway leading Gibson to stardom.