Marvel Two-In-One was a American comic book series published by Marvel Comics that featured the Fantastic Four member, the Thing, in a different team-up each issue with a different character. The series continued from the team-up stories starring the Thing in the final two issues of Marvel Feature (1971 series), and lasted for 100 issues, from January, 1974, through June, 1983. Seven annuals were also published. As the series progressed, many of the characters paired with the Thing were more obscure superheroes (or, on occasion, supervillains). Although popular, the series never attained the commercial success of Marvel Team-Up, which featured Spider-Man in the same format of different guest stars each month.
Marvel Two-In-One ended with a "team-up" between the Thing and Ben Grimm, his own human alter ego, in issue 100; this team-up was enabled by the Thing travelling to a parallel timeline in which he was not the Thing. The alternate Ben Grimm seen here had first appeared in Marvel Two-in-One #50. Immediately following the cancellation of Marvel Two-In-One, the Thing was given his own solo title, sans team-ups, in which the Thing decided to leave the Fantastic Four and remain on the Beyonder's alien planet where he could control the transformation to his rocky form.