To some, President Andrés Manuel López Obrador of Mexico is a reformer who steered the country toward progress during his six-year presidency. To others, he’s a bulldozer who eroded democratic institutions, and is leaving a host of problems for his successor.

Still, as he comes to the end of his term, his critics and supporters largely agree on one thing: Mr. López Obrador transformed his nation — more so than any other leader in the country’s recent history.

“This is definitely a watershed presidency that has changed the direction of the country,” said Andrew Paxman, a historian at Mexico’s Center for Research and Teaching in Economics, who is writing a biography of Mr. López Obrador.

Blending populist rhetoric with hard-line tactics, Mr. López Obrador expanded his own influence. Over the last decade, he has forged a political movement that mirrored his own personal grievances and tapped into the public’s desire for change. Fusing nationalist and leftist ideals, he vowed to bring change to this country of 130 million.

And in many areas, he then delivered on that pledge, and is now leaving office with approval ratings above 70 percent.

On Tuesday, Mr. López Obrador will step down and hand the mantle to his longtime protégée, Claudia Sheinbaum, a former mayor of Mexico City. The landslide win in June by Ms. Sheinbaum — Mexico’s first female president — was seen by many as a clear vote of confidence in Mr. López Obrador and Morena, the party he founded in 2014. June’s elections also gave Morena large legislative majorities unseen in Mexico since the transition to democracy in 2000.