Transformer

The Transformers were an alien race from the planet Cybertron, which exists somewhere in the Multiverse, or perhaps even in a distant galaxy. A race of sentient robots with the uncanny ability to turn into Earth vehicles such as Cars, Planes and Trucks, Transformers have the ability to hide in plain sight.

Transformers are split into several factions, but the most noteworthy are the Autobots and Decepticons, both of which have found their ways in Equestrian affairs. In particular, Optimus Prime and Megatron are big deals, whose battles are known across the multiverse, and have affected it in many ways.

The Transformers vs G.I. Joe
During a huge war, Megatron was defeated by Optimus Prime and was sent to the world where Magic is Friendship, where he was licked by Moon Dancer.

Friendship is Magic
At some point, Jazz, Bumblebee and Optimus Prime found themselves in Ponyville, Equestria. Rainbow Dash is buds with Starscream

Megatron, and Dan Mandel all sung about how much they loved the summer.

Bumblebee and Optimus Prime appeared at the Summer House Party with the ponies and various other figures.

When Megatron and Cobra Commander stole the Matrix of Leadership, Optimus Prime was aided by Twilight Sparkle, and Pinkie Pie wielding a giant NERF gun who helped defeat the tyrannical duo. Optimus later admitted that friendship really was magic.

Ask Vector Prime
Vector Prime admitted that was among the most evil beings he ever found in the multiverse, comparing him to entities such as Logos Prime, Liege Maximo and Megatronus.

Ask Sideways
Sideways once "drank" Discord under a table at Maccadam's Old Oil House.

AllSpark Almanac
Discord hung out at Maccadam's Old Oil House with other Transformers.