Land, Sea, Sky

A type of trio. Also a form of Elemental Rock-Paper-Scissors, in which the three elements of Earth, Water and Air are made a trinity.

Land is usually depicted as steady and stable, Sea as unpredictable, and Sky as free spirited. Land may also involve death because of burials, and sky will often be the "king," especially in works created before human flight, since no matter where you are, you're always under the sky. The "sky is king" motif has become less common since flight became a thing, however.

Sea is usually depicted as the most hostile of the three; considering most of the time humans are at sea, they're on a pretty small (relatively speaking) ship, and at the mercy of the extremely unpredictable sea, which could decide to throw storms, whirlpools, tsunamis and other unpleasant things at you at any moment, this is hardly surprising.

In an Elemental Rock-Paper-Scissors setting, expect Sea to overcome Land, Land to overpower Sky, and Sky to defeat Sea.

These are considered to be the three classic Theatres of War, each with its own branch of the military (Army, Navy, and Air Force respectively) specialized to fighting in it.

See also Four-Element Ensemble and Fire, Ice, Lightning, another common elemental trio.

Anime & Manga

 * The Bigs from The Big O fit the common characterizations of their spheres; Big O (land) Big Duo (sky) Big Fau (sea)
 * Magmatron from Beast Wars Neo has his units Landsaur, Skysaur and Seasaur.
 * In Bleach, there's a subtle name theming referred to these three elements in the Shiba siblings: Kaien (Kai = Sea), Ganju (Gan = Rock, hence earth) and Kukaku (Ku = Sky).

Classical Mythology

 * The Three Great Beasts, Behemoth (Land), Leviathan (Sea), and Ziz (Sky).
 * In Greek Mythology, Zeus got land and sky, Poseidon got the ocean, and Hades drew the short straw for the Underworld.
 * Also, there are the primordial gods Gaia (the earth), Uranus (the sky), and Pontus (the sea). Gaia, the first and born out of Chaos, conceived Uranus and Pontus via parthenogenesis, and then mated with them. Most notably, the Titans and Greek pantheon were the byproduct of her union with Uranus. Additionally, Tartarus (the hell-pit) was sometimes perceived as a primordial deity/force of nature.
 * A common referent in Celtic Mythology.

Comic Books

 * The Terrible Trio, a group of Batman villains introduced in the Silver Age, were criminals wearing masks of animals: Fox (Land), Shark (Sea) and Vulture (Sky).
 * The big three Marvel (or rather, their predecessor Timely) heroes of World War II: Captain America (comics) is Land, Namor is Sea, and Human Torch (Jim Hammond, not Johnny Storm) is Sky.

Literature

 * In Julian May's continuity of the Black Trillium series, there are three Archwizards: of the land, sea, and sky. Binah, the only non-evil sorceress in the original book, is retconned as the Archmage of the Land.
 * In the end of Quenta Silmarillion, all three of the eponymous Silmarils are distributed equally across the sky (Earendil's Silmaril), earth (Maedhros'), and sea (Maglor's).

Live-Action TV

 * Very common in Super Sentai and Power Rangers series, such as Taiyou Sentai Sun Vulcan (Vul Eagle = air, Vul Shark = sea, Vul Panther = land). The most important position, that of the Red Ranger, is usually the one with sky.
 * The Hayate/Wind Ninja Academy in Ninpuu Sentai Hurricanger/Power Rangers Ninja Storm teaches these three disciplines, and the three core Rangers each wield one. Interestingly enough, the Rangers that join the team later use different abilities altogether (the next two, from a rival academy, use Thunder; and the sixth is either Fire or Non-Elemental depending on which show you're watching).
 * Tensou Sentai Goseiger has a team of two Rangers of each, though one of the sea Rangers was killed off in the backstory. Gosei Knight uses all three.

Video Games

 * The transformations in The Legend of Zelda Majoras Mask; Deku is air (flower helicopter), Goron is land (stone rolling), Zora is Sea (dolphin swimming).
 * Also used in The Wind Waker; the first three MacGuffins are collected from the sky spirit Valoo, the earth spirit the Great Deku Tree, and the sea spirit Jabun.
 * Three of the Four Guardians of Neo Arcadia in Mega Man Zero fit this mold. Each functions as the military general of their own unit: Sage Harpuia commands the Rekku Army (the air force), Fairy Leviathan is leader of the Meikai Army (the navy), and Fighting Fefnir controls the Jin'en Army (the army). This is off-set partially by the fourth Guardian (Hidden Phantom) and his Zan'ei Army, which was Neo Arcadia's stealth force and anti-Resistance intelligence unit.
 * Pokémon Ruby and Sapphire: Groudon (land), Kyogre (sea), and Rayquaza (sky), all of which were based on the aforementioned Three Great Beasts.
 * It has another one in the form of...berries, surprisingly enough. Three especially rare berries: Liechi, Ganlon, and Salac, are described to contain the power of the sea, land, and sky respectively.
 * One fan used this trope to describe the three Pokémon he defined as the only truly Chaotic Evil Pokémon: Tyranitar (land), Gyarados (sea) and Hydreigon (sky).
 * Resident Evil 5: the Earth, Sea, and Sky Emblems used to open a gate in one level.
 * The Theme Naming convention for Sora (sky), Riku (land), and Kairi (sea) along with Ventus (wind), Terra (earth), and Aqua (water) in Kingdom Hearts. To a lesser extent, Roxas (An anagram of "Sora" with an X added, while also meaning "red" itself, so could be interpreted to be "twilit Sky"), Axel/Lea (Meadow) and Xion (Shio=Tide).
 * Mitsumete Knight R: Daibouken Hen has the Slates of Earth, Sea and Sky. Scattered throughout the world, you need to gather them and put them all in a machine inside in order to activate the Warp Whistle system.
 * Used in one of the riddles in Batman: Arkham City. Although the wording suggests the classic military interpretation.
 * In the Baten Kaitos series, the three objects used to seal Malpercio are the Earth Sphere, the Ocean Mirror and the Sword of the Heavens, when the sealing is shown in the 2nd game the line ", accursed one, for the sake of the earth, the sky and the ocean, thy life must end!" is used. Of note is that during the games , the earth "polluted and barren", the ocean is sealed away ("and the Lost Ocean") and the lower part of the sky filled with the poisonous "taintclouds".
 * In Advance Wars 2: Black Hole Rising, the three Green Earth commanders fit: Eagle has stronger air units and is the proud leader of the trio, Jess has strong ground vehicles and tends to be very practical (her resupply power actually makes her pretty handy with air and sea units despite the attack power penalty she suffers with them), and Drake specializes in naval warfare and has very damaging CO powers.
 * In Clock Tower 3 at one point Alyssa must solve a riddle involving the three rooder's stones of Earth, Sky and Sea. To be specific, she must put them in the right order to free some ghosts.

Western Animation

 * Centurions features Max Ray ("brilliant sea operations commander"), Jake Rockwell ("rugged land operations specialist") and Ace McCloud ("daring air operations expert").