WebKit is a rendering engine which is one of the major components of a web browser. Chrome/Chromium was released in 2008 using a modified version of WebKit as its rendering engine. Eventually in 2013 they created a fork of WebKit called Blink, which is the current rendering engine for Chrome/Chromium.

Chromium was still the base before the WebKit/Blink fork. Chrome and Chromium were released simultaneously in 2008.