The pundits rarely put Trump and William Jennings Bryan in the same sentence, and for very good reasons: Bryan was a passionate left-wing lawyer and politician who viewed political and economic questions largely in moral terms; while Trump is a semi-successful developer and mass marketer with no interest in traditional Christian values and a predominantly right-wing agenda. Bryan would have seen Trump as the personification of all of the vices that he was fighting against; Trump would have dismissed Bryan as a loser.
That said, in functional terms, both of them were populists who engineered hostile takeovers of their respective parties, to the horror of the prevailing establishment. Bryan never succeeded in getting elected; let’s hope Trump suffers the same fate.