There is a new Hamilton in “Hamilton,” although President Obama and Beyoncé have seen him already.

On Monday, Javier Muñoz replaces Lin-Manuel Miranda, and steps into the title role of the biggest Broadway show in years, playing the nation’s first Treasury secretary, Alexander Hamilton.

He is not exactly new to the role. Over much of the last year, Mr. Muñoz has relieved the star once a week, and on other days watched the production from a stool just offstage, waiting in case Mr. Miranda ever took a tumble. (He did not.)

Already, he has a reputation and a fan base. He’s been described as the sexy Hamilton because of the swagger he brings to the role, and Mr. Miranda bestowed on him a hashtag-nickname, Javilton, that has stuck.

Mr. Muñoz has some obvious similarities to the man he is replacing — both have parents from Puerto Rico, graduated from New York City public schools and encountered Broadway as children, becoming passionate about theater. And their careers have been entwined for years — Mr. Muñoz was Mr. Miranda’s alternate, and then his successor, on “In the Heights,” and has been his alternate throughout the development of “Hamilton.”