Mister Fantastic is a Marvel Comics superhero who is the leader of the Fantastic Four. He has the ability to manipulate his body by stretching and shaping it to any shape he desires. As scientist and inventor Reed Richards, he is widely acknowledged as a super-genius and one of the most intelligent people on Earth.

A child prodigy, Reed Richards obtained several degrees by the time he was a teenager, from such prestigious universities as the California Institute of Technology, Harvard University, and Columbia University. While at Columbia, he met a brilliant fellow student, Victor Von Doom. In Richards, Doom had met the first person who could rival him intellectually; regarding Richards as his ultimate rival, Doom became increasingly jealous of Richards. Determined to prove he was better, Doom conducted reckless experiments which eventually scarred his face and would lead him to become Doctor Doom.

Some time afterwards, it was on Reed's initiative that the fateful space mission which had Susan Storm, Johnny Storm and Ben Grimm accompanying him into space took place. In space, they were exposed to cosmic radiation; when they crashlanded and found that their bodies were changed dramatically, it was Mister Fantastic's suggestion that they decided to use their new abilities to serve mankind as the Fantastic Four.

To that end, he created numerous exotic devices and vehicles for the team to use such as clothing made of 'unstable molecules' so that it can be used with their powers safely. Furthermore, he often leads the team into daring expeditions such as into the Negative Zone in addition to opposing evil. In addition, he has felt personally responsible for Ben Grimm's grotesque change and has laboured off and on to reverse it permanently.

Unfortunately, there are drawbacks to his association with the team. Chief among them is that the team's violent encounters with Doctor Doom are on account of his irrational grudge against Reed for supposedly sabotaging his college experiment that scarred him.

Mr. Fantastic will be played by Ioan Gruffudd in the forthcoming feature film.

In Neil Gaiman's 1602, his power is associated with the classical element of water.