Meat Puppet

"I'm not too fond of getting my hands dirty; instead, I take over the minds of others. They do everything I say, like good little puppets."

—Jov Leonov, Psi Ops the Mindgate Conspiracy

Not to be confused with People Puppets, a Meat Puppet is a biological and (usually) living Host that has been taken control over by a Puppeteer Parasite, Body Snatcher or similar character, be it through science or occultic sorcery. The attempt to control a potential Meat Puppet in such a manner either results in Body Control, Mind Control or Demonic Possession. Compare to Empty Shell.

The purpose of a Meat Puppet is usually to act as a tool for the controller, ranging from basic slaves to intricately placed spies, sometimes also being used as a "Seeing Eye Dog" if the controller can remotely view through the puppet's senses. Generally, a Meat Puppet is a Faceless Goon, used as a Meat Shield or simple becomes a brainwashed Mook that's expendable to a villain or antihero in control of it.

The following are special types of Meat Puppets chosen for specific purposes:

Big Dumb Body - A meat puppet that holds little intelligence, but is desirable for its physical prowess and durability.
Living Bodysuit - when a host is chosen as a disguise for reasons of secrecy and espionage.
Wetware Body - a biological body possessed by a computer.
Willing Channeler - a Host who "wants" to be controlled, or at least isn't against having his/her body used by someone (or something) else.

An entirely alternate meaning refers to The Internet and New Media culture in social media: an online "entourage" or crowd of Yes People surrounding a particular internet user and/or a "personal army" of internet users recruited to attack or defend someone in a Flame War or flare of Internet Backdraft, or to promote them or their product. This is connected to Astroturf except that Astroturf is usually for a politician or product or company, while a Meat Puppet can appear anywhere (and are often why a debate escalates to Flame War, Internet Backdraft, or appearing on Fandom Wank levels.) These are usually called Meat Puppet as opposed to Sock Puppet, because they are actually separate people, unlike a Sock Puppet, which is a different user identity (or collection of them) created by the same person. That said, good luck in telling them apart - especially in places that allow anonymity and don't ban proxies.

Examples of Meat Puppet include:

Film

The avatar Na'vi bodies in Avatar
In the much-maligned sequel to the film adaptation of Starship Troopers, Control Bugs take over an entire outpost of Mobile Infantry soldiers and pit them against the main characters.
Done rather disturbingly by The Devil in The Dark Side of the Moon to the crew of a space ship.

Literature

Any controller in Animorphs

Toys

The Krana in Bionicle can control a being once attached to his or her face. If they possess a Matoran, it's a straight example of the trope, since Matoran lapse into unconciousness when separated from their Mask of Power. However, if they possess a Toa, there will be a struggle for control between Krana and host. "I Know You're in There Somewhere" Fight ensues.

Video Games

Geist surrounds itself in having the player possess hosts both biological and machine to affect the living world and defeat The Big Bad. There's even a minigame devouted to Ghosts vs Hosts.
Psi Ops the Mindgate Conspiracy refers to mind controlled soldiers (under the terrorist group: The Movement) as Meat Puppets, and is the trope namer in this case.
Painkiller also contains a character who uses mind control to manipulate potential enemy hosts, (and sometimes including allies).
The Half Life series features various types of headcrab creatures that overlap with Zombie Mooks. The headcrabs apparently latch onto the skull of the host, eat their way through it, and then control the new "corpse" while simultaneously mutating it to make it even nastier.
The Flood parasites of Halo insert their tendrils into the nervous systems of their host subjects. Afterwards, they control and mutate the host in the same way that headcrabs do.
In Mario & Luigi: Superstar Saga, after defeating Cackletta, her defeated spirit takes over the beaten-up body of Bowser and becomes... Bowletta.
Mass Effect 2: ASSUMING DIRECT CONTROL
Ghost Trick: Yomiel can possess and manipulate living creatures the way Sissel manipulates inanimate objects. Aside from his cat the hosts are either unknowing or unwilling, but he can also possess the Empty Shell of his own corpse.
This is the implied case with Millennia from Kagero: Deception II. She never speaks in cutscenes aside from nodding or shaking her head, but exactly how much control the Timemoids are exhibiting over her is up to the player via Dialogue Trees.
Meat Puppet: Yes, there is a game whose title is the same as this trope, and the game mostly follows the description at the top. Lotos/Lotus Abstraction answered a personal ad that said about "nocturnal missions". She is being controlled by The Puppet Master/Martinet. She is required to make Asshole Victims out of six leaders of the most profitable corporations (also known as ambassadors), and do this in one night, or else the suit that was put on her against her will will self-destruct and kill her! This is what Martinet is trying to accomplish: The Puppet Master wants to use Lotos to reassemble the fractured genetic key to universal entropy and shut down the universe. That would make Lotos accomplice to the biggest murder of all time a prospect that displeases her greatly. She'd rather save the world instead. You can find out more here.

Webcomics

In Fite!, the Mutali turns out to be just puppets of Skerry.

New Media

The alternate definition mentioned above, the "internet entourage," is a fairly common sight in some places, as anyone who posts a rant about, say, Justin Bieber will very much find out.