Jean Gray is a household name among fans of comics as well as the general public. Magneto is seen repeatedly fighting to seize his power in the X-Men series. Even the most powerful apocalypse, one of Xman's most formidable enemies, has been seen to give in to Gene Gray. Gene Gray, owner of Phoenix Force, is much more powerful in comics. The ability to keep oneself alive has given him unique strength. Gene can defeat Thanos in a relationship with the Phoenix Force as well as his cosmic power.
But these are just stories of losing Thanos. Thanos with six Infinity Stones is much more powerful, much more terrifying. In a word, it is impossible to defeat Thanos alone if these stones are captured somehow.