(written from a Production point of view)
Mego Toys (pronounced MEE-go) was popularly known as a major producer of licensed action figures in the 1970s and early 1980s and produced the first action figures stemming from the Star Trek live-action franchise.
The company began to produce "dime-store" dolls and other toys in 1954. Beginning in 1971, Mego created the first 8" action figure called Action Jackson to compete with Hasbro's well-established G.I. Joe line. Mego produced the World's Greatest Super Heroes (WGSH) line of licensed DC and Marvel comic figures beginning in 1972. Space: 1999, Planet of the Apes, and Wizard of Oz figures were also popular products.
Star Trek affiliation
Mego also produced 3-3/4-inch Star Trek: The Motion Picture action figures, 8-inch starships, and assorted toys in 1980. However, due to disappointing sales and the failure of their bid to license and produce Star Wars toys, Mego declared bankruptcy in 1982 and closed their doors in 1983.
British toy company Palitoy was the exclusive UK distributor of Mego's Star Trek toys, figures, and accessories.
Interaction with Star Trek parody and pop culture productions
In the Star Trek parody and pop culture-referencing television sitcom The Big Bang Theory, Mego Star Trek action figures have made appearances on a few occasions. This comedy series is centered on four science nerds who are rabid fans and collectors of Star Trek, science fiction, and comics memorabilia.
Mego toys appeared prominently in the "The Transporter Malfunction" episode in which central character Sheldon Cooper and his roommate were given a rare, mint-in-box (a condition highly valued in toy collector circles) Palitoy "Star Trek Transporter Room Playset" as a gift by their attractive female neighbor. This toy is a variant of Mego's "USS Enterprise Action Playset" and was seen as a generous gift indeed as this UK-exclusive version is considered to be exceptionally rare. 
Sheldon initially refused to play with it to avoid diminishing its perceived value but he quickly yielded to temptation, goaded on by his Mego Spock action figure which had started to "speak" to him. Spock's voice was performed by Leonard Nimoy. Sheldon accidentally broke the toy then surreptitiously replaced it with his roommate's. Later, in his fevered, guilt-ridden imagination, Nimoy's "Mego Spock" chastised him for his dastardly deed and subsequent refusal to own up to it. His initial resistance caused Sheldon to be attacked by a Mego Gorn figure in a nightmare and he finally confessed his guilt to his roommate.
The items used in the episode were taken from CBS Television Studios's Licensing Department Archive. CBS is not only the producer of The Big Bang Theory but is also the owner of the Star Trek television franchise.
Mego Star Trek Action Figures
The very first Star Trek action figures were produced by Mego starting in 1975, were eight inches tall, and were fully articulated with cloth replica uniforms and miniature accessories. Most were good likenesses of the show's characters, while others were obvious "rush jobs" or re-sculpts of figures from other Mego toy lines.
In total, fourteen figures in three "waves" were eventually released by Mego between 1975 and 1978. The second and third "Aliens" waves are the hardest to find, with the Romulan and Andorian from Wave Three considered to be the rarest of all.
In 2007, EMCE Toys began to release faithful reproductions of many of Mego's 8-inch Star Trek figures and have supplemented the line with several new additions. The USS Enterprise bridge playset was also re-released. EMCE Toys' "Star Trek Retro Cloth Figures" and the playset are distributed by Diamond Select Toys.
Wave One Figures
This wave originally consisted of these five figures:
- Captain James T. Kirk (with belt, phaser and communicator)
- Mr. Spock (with belt, phaser, communicator and tricorder)
- Mr. Scott (Scottie) (with belt, phaser and communicator)
- Dr. McCoy (Bones) (with belt, phaser, communicator and tricorder)
- Klingon (with belt, phaser and communicator)
Later, as part of the same set, Mego added:
Wave Two Figures ("Star Trek Aliens")
- Neptunian (lizard-like aquatic alien with scales and webbed wings; never appeared in Star Trek; no accessories)
- The Keeper (actually more styled after Balok's "puppet" in a white robe; no accessories)
- The Gorn (in fact, a brown re-cast of the Marvel Heroes' LIZARD figure head on a Klingon figure body; with black plastic belt and phaser and communicator in red plastic, same as the Klingon figure)
- Cheron (presumably styled after Bele; entire body and costume is half-black/half-white; no accessories)
Wave Three Figures ("Star Trek Aliens")
- The Romulan (with gold "vac-metal" helmet, black belt, and "Klingon red" phaser and communicator)
- "Talos" (Talosian in yellow jumpsuit with black collar and orange boots; no accessories)
- Andorian (in standard Andorian outfit as seen in "Journey to Babel"; no accessories)
- Mugato (oddly CLOTHED in green top - which may have faded to yellow - with black belt and red pants; no accessories)
Figure Playsets and Accessories
In addition, several playsets and accessories were produced for the figures:
- U.S.S. Enterprise Action Playset (a mock-up of the Enterprise bridge with Captain's Chair, Navigational Console, two "Crew Seat" stools and "spinning" Transporter; doubled as storage case for figures]
- U.S.S. Enterprise Action Gift Set (essentially, the above playset with the original five "Wave One" figures (no Uhura)
- Mission To Gamma VI (the rarest of the playsets; recreation of Vaal from "The Apple"; came with four generic alien figures)
- Telescreen Console (actually, a tabletop game that doubled as an "add-on" piece for the Action Playset; game screen with Captain's Chair and Control Lever)
Other Mego Star Trek Toys
Star Trek Communicators
Sold in both a boxed set and a carded "blister pack", this was a pair of walkie-talkies styled after the communicators seen on the original Star Trek. They were molded primarily from blue plastic, with a button-release "cover" that flipped up like the antenna grid on the original prop.
Command Communications Console
Super Phaser II Target Game
This was a "role playing" toy that consisted of a light-emitting "Super" type 2 phaser (an enlarged, bulkier version of the standard type 2 phaser) with a "sonic buzzer device" that fired at a "target reflector badge" depicting a Klingon D7 class cruiser. Firing at the badge's large red target reflected the light back to the phaser, activating a buzzer.
Star Trek Tricorder
This was an actual, functioning portable tape recorder made to look like a tricorder prop from the show. Like the communicators, this was molded primarily from blue plastic. It had a flip-up top that concealed the dial that controlled most of the recorder's functions, as well as the volume control. The tape compartment was located directly below. The unit came with a cassette tape containing 30 minutes of audio from "The Menagerie, Part I" and "The Menagerie, Part II". The other side of the tape was blank, allowing the user to create their own audio recordings.
Star Trek Phaser Battle
Similar to the "Telescreen Console" marketed with Mego's original Star Trek action figures, this was a tabletop game unit that allowed the player to attack alien ships. Gameplay was a little more complex that the Telescreen, as there were more controls (especially dual buttons for port and starboard shields) to use, as well as a larger playing screen and a "digital-style" scoreboard.
Star Trek Educational Toys
Mego marketed a line of educational Trek-related toys which included an Intergalactic Projector (a home planetarium projector), a Crystal Radio set, and other "build-it-yourself" scientific toys.
The company advertised a tribble toy but it is doubtful that it ever reached production.