Leviathans

"J.A.R.V.I.S., you ever heard the tale of ?" "I wouldn't consider him a role model."

- Iron Man and J.A.R.V.I.S.

Leviathans are intergalactic beasts and warships for the Chitauri.

Invasion of Zen-Whoberi
Along with the Black Order and a contingent of Chitauri soldiers, the Leviathans followed Thanos to Zen-Whoberi. There they successfully aided the Titan in his goal of slaughtering half of the Zehoberei population.

Chitauri Invasion
"I'm bringing the party to you." "I -I don't see how that's a party."

- Iron Man and Black Widow

The Leviathans were used by the Chitauri during their assault on Earth as both warships and assault crafts. They roam the Sanctuary, and one such beast was straddling along the perimeter of the asteroid upon which Loki and The Other were having a discussion regarding the Tesseract. During the Battle of New York, the first Leviathan that arrived on Earth was initially confronted by Iron Man, who caused it follow him to where the rest of his team was, and was destroyed by both him and Hulk.

Other Leviathans arrived from the dimensional portal and attacked New York City, but were countered and destroyed by the Avengers. Many more Leviathans were ready to attack, but once the Chitauri Command Center was destroyed by the nuke sent in by S.H.I.E.L.D. that Iron Man diverted through the portal, every Chitauri, Leviathans included, fell to the ground and died.

Aftermath
One of the Leviathans that had fallen was photographed. The fall had killed hundreds of people. The photograph was used by the New York Bulletin, headlining its "Battle of NY" coverage. One corpse fell inside a building not far away from Stark Tower. Adrian Toomes' salvage company was contracted by the city of New York to salvage the technology from the corpse, but they were interrupted and ordered to hand over all the recovered tech by the Department of Damage Control.

Scarlet Witch's Illusion
"Guys, I got Strucker." "Yeah... I got something bigger."

- Captain America and Iron Man to the Avengers

One Leviathan corpse was recovered by S.H.I.E.L.D., and was eventually secretly stolen by Wolfgang von Strucker's HYDRA cell and placed in the HYDRA Research Base. Over the next year Strucker and his scientists studied the corpse, obtaining several Chitauri technology pieces, especially the anti-gravity technology later incorporated into the Chitauri Armor from it. In 2015, during a battle in the facility between the Avengers and HYDRA, Scarlet Witch used her powers to trick Iron Man into believing that the Leviathan was actually still alive, and showed him visions of the dead Avengers and the Chitauri and Leviathans crossing a wormhole towards Earth, presumably to invade it.

Allies

 * Chitauri - Passengers
 * Thanos - Master
 * Black Order
 * Ebony Maw † - Commander
 * Gamora †
 * The Other †
 * Loki † - Former Commander

Enemies

 * Zehoberei
 * Gamora's Mother †
 * Avengers
 * Tony Stark/Iron Man
 * Bruce Banner/Hulk
 * Steve Rogers/Captain America
 * Natasha Romanoff/Black Widow
 * Thor
 * Clint Barton/Hawkeye

Appearances
In chronological order:
 * Avengers: Infinity War (flashback)
 * The Avengers
 * Spider-Man: Homecoming (flashback)
 * Daredevil
 * Season One
 * Rabbit in a Snowstorm (picture)
 * Daredevil (picture)
 * Nelson v. Murdock (picture)
 * The Ones We Leave Behind (picture)
 * Avengers: Age of Ultron (corpse and vision)
 * Daredevil
 * Season Two
 * Seven Minutes in Heaven (picture)
 * A Cold Day in Hell's Kitchen (picture)
 * The Defenders
 * Season One
 * Take Shelter (picture)
 * Captain America: Civil War (footage)
 * The Punisher
 * Season One
 * Two Dead Men (picture)
 * Front Toward Enemy (picture)
 * Daredevil
 * Season Three
 * Please (picture)
 * Blindsided (picture)

Trivia

 * The "Leviathans" share some similarities with the Midgard Serpent, a recurring villain in Thor comics, often at Loki's service.
 * Leviathans are original creations by Zak Penn and Joss Whedon.
 * In concept art for The Avengers, the Leviathans are listed as "Chitauri Jumbos".
 * In the film commentary, it was mentioned that "jumbo" was the creatures original name. However, it was decided to change it to Leviathan as "jumbo" would be too silly if it was made into a toy.