He was England's MOTS in 2015, 2 tons and 2 50s. But while Smith, and Rogers, scored a few more runs, how, where and when Root got his was more impressive.
By close of day 1 in the 4th Test, in bowler friendly conditions, he had more than doubled Australia's 1st innings score and remained not out.
In the 1st Test, he came in with England at **** all for three and scored 130-odd.
No century at Edgbaston, the other game England won, but he was 90ish for once out in a fairly low scoring game.
He did bugger all on the flat London tracks, one of which was a dead rubber, but given the series ended 3-2, he was pretty much the difference. I would consider that series defining.