0 is the highest # ever or 99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
There is no "highest number". It just keeps going on and on and on... That's why they have an infinity sign. In the 1980's though, a guy named Ronald Graham was in the Guiness World Book of Records for having the "highest number ever used in a serious mathematical proof". They called it "Graham's number". I sooo want a number named after me.