He was a member of the Second Triumvirate, along with Mark Antony and Octavian. While Julius Caesar defeated Pompey and while Mark Antony defeated Brutus, he single-handedly ruled over the city of Rome.
The wikipedia article on him is five short paragraphs, barely half a page. It doesn't explain who he was, how he rose to power, or how he fell from it. When you google him, the third result is the wikipedia page on Mark Antony.
So, who was he? How did he rise to and fall from power? Why did Julius Caesar, Mark Antony, and Octavian all trust him so much?
I asked the same question to myself once. After watching HBOs Rome.
So I read a lot of wikipedia and it took my far longer that it should have to take in that ML was Caesar's Master of Horse, and the #2 man in his 10 yearish rule of the Republic. He ruled as a triumvirate with Octavian Caesar's heir, and Mark Anthony his top general.
The other things that took me to far longer to comprehend, was at this time Octavian was still in his 20s and not old enough by Roman standards for even the first rung on the Cursus Honorum. Anthony, had been left in charge of Rome back during the Civil war but made such a mess of things that Caesar had to remove him. At the time of the first Triumvirate, Lepidus would have been the elder statesmen of the group, and represented continuity of governance and stability in the city of Rome and to the Roman elite.