Board Thread:Questions and Answers/@comment-10952853-20130617015352/@comment-2211792-20130617044159

Yamamoto was still stronger than Yhwach. When they fought 1000 years ago, Yhwach didn't have his bankai-stealing medallion and got his ass delivered to him (and Yama-jii's bankai wasn't complete back then). Yhwach won this time only because of the medallion.

However, Ichigo and Kenpachi have received massive power-ups, so one of the two of them may very well claim the title of the strongest character in Bleach.