Short answers, pulled from the story.
The Forgotten Realms is the most popular D&D campaign setting. Created by Ed Greenwood as his personal campaign and first published by TSR in 1987, it has been described by author Sean Patrick Fannon as "may be the most widely played-in game setting in RPG history." It is the default setting for most adventures released for the 5th edition of D&D.
Blackmoor, created by Dave Arneson in 1971, was the original D&D campaign setting, built before Dungeons & Dragons itself existed. Arneson created it for personal games using the Chainmail rules set, predating both Greyhawk and the publication of D&D. The D&D Blackmoor supplement was published in 1975.
Keith Baker won a fan contest held by Wizards of the Coast in 2003, with the prize being a publishing contract. The Eberron campaign setting was released in 2004, featuring a world of pulp action and fantasy noir with steampunk influences where magic substitutes for technology.
Dark Sun, released by TSR in 1991, is set on the post-apocalyptic desert world of Athas, stripped of life by the uncontrolled use of defiling magic. It inverts standard D&D conventions: psionics are as common as magic, arcane spellcasters are rare and despised, and familiar races like elves and halflings take radically different forms. The setting drew heavy inspiration from the novels Dune and the Barsoom series.
Matthew Mercer created Exandria in 2012 for personal campaigns, and it became the world of the Critical Role web series. After roughly a year and a half of collaboration between Mercer and Wizards of the Coast, Exandria officially entered D&D in 2020 through the Explorer's Guide to Wildemount. Exandria first appeared in an official Wizards publication in the 2019 adventure Baldur's Gate: Descent into Avernus.
Between 2016 and 2018, James Wyatt released six unofficial "Plane Shift" PDF articles adapting Magic: The Gathering planes for D&D: Amonkhet, Dominaria, Innistrad, Ixalan, Kaladesh, and Zendikar. These were followed by the official full hardcover Guildmasters's Guide to Ravnica in 2018 and Mythic Odysseys of Theros in 2020. Theros originated as a Magic: The Gathering block released in 2013.