Mother Nature

The arch-Nature Spirit of Earth... or whatever planet is the story's setting. May or may not have a humanoid form (substitute "humanoid" with whatever species equivalent in non-terrestrial settings), but if it is, it's Always Female due to Mother Nature, Father Science.

Of course, if you actually look at old cultures Mother Nature tends to occur mainly in fertile places, and infertile parts of the world often had male Earth deities. Egypt had Geb, for instance, and the Norse had Ymir and Frey.

Often a bona fide Physical God, if not outright one of the Powers That Be. Actually pissing her off is likely to result in Gaia's Vengeance, while making her sad can result in Gaia's Lament.

Advertising

 * There was a commercial campaign for Chiffon margarine in the 1970s that had a Mother Nature. "It's not nice to fool Mother Nature!" *thunderclap*

Comic Books

 * Gaea from Marvel Comics.
 * Dilbert has met her. She's a jerk.

Fan Fiction

 * Terra, the Mother Goddess of the Mythology 101 Cycle, who is the Ethical Slut version.

Films -- Animated

 * Mother Nature presides over the wedding in The Santa Clause 2.
 * Mother Nature (voiced by Phyllis Diller) appears in the Filmation Snow White sequel Happily Ever After.

Films -- Live-Action

 * Mother Nature is a character in the Christmas Special The Year Without a Santa Claus.
 * From the 2009 film Avatar, we have Eywa, Pandora's equivalent of Mother Nature.

Literature

 * Yavanna in The Silmarillion.
 * In Simon R. Green's novel Drinking Midnight Wine the chracter of Anthropomorphic Personification of nature and earth.
 * The various Ladies from the Repairman Jack novels.

Religion and Mythology

 * The "mother (earth) goddess" figures in many Real Life religions and mythologies.
 * Gaia, the mother of the Titans and greek gods. Note that she's usually cast as a villain, though.
 * The Poetic Edda has Gerðr, a giantess courted by Frey with the aid of Skirnir. The story is part of a fertility ritual in which Gerðr represents Earth, Frey fertility, and Skirnir sunlight.

Role-Playing Games

 * Sakiko on Honorable Hogwarts. Invoked Trope.

Video Games

 * Final Fantasy VII's Planet, and its supposed Anthropomorphic Personification, Minerva, from the Compilation sub-franchise.
 * In Pajama Sam, Mother Nature is the president of World Wide Weather.
 * Animebona is the spirit of the eponymous planet in Albion, and the entity representing magic in Dji-Kantos philosophy.

Western Animation

 * Gaia, the spirit of the Earth, from Captain Planet.
 * A matronly Mother Nature is a Recurring Character on The Smurfs.
 * It was Mother Nature who gave Super Ted his powers.