Washington Mutual (WaMu) was a large savings and loan association that was seized by the Federal Deposit Insurance Corporation (FDIC) in September 2008 due to the financial crisis.
JPMorgan Chase & Co. (Chase) acquired the majority of WaMu's assets, including its banking operations, but it did not become WaMu. The FDIC created a new bank called "Washington Mutual Bank, National Association", which was then sold to JPMorgan Chase.
So, WaMu ceased to exist as a separate entity, and its assets and banking operations were absorbed by JPMorgan Chase. However, WaMu did not "become" Chase. They are separate entities with distinct histories.