Lepidus was a ranking politician in Rome, and was intimately connected to the families involved in the post-Sulla power struggle. He was married to Junia, sister to Brutus and also sister to the wife of Longinus. Brutus and Longinus famously murdered Caesar, but Lepidus was a major ally of Caesar's and fought against the "Liberatores" after the assassination.

Lepidus was known as a skilled negotiator and military commander, who managed to keep the peace and keep Rome from falling apart after the assassination. Without going into too much detail, the power grab ended up a pitched struggle between Octavian/Antony (Caesar's heir/one of Caesar's foremost military commanders) and Cassius/Brutus (Caesar's rival, absurdly wealthy and politically powerful/Caesar's adopted son). Lepidus turned over control of most of his legions to Octavian/Antony during the war, and as a result began to fade from power.

He has been treated poorly by historians for seeming to be so easily bullied by Octavian/Antony, and he did agree to execute Cicero, as well as his own brother Paullus, for being supporters of Caesar. Later, Lepidus was removed from office and a few poor political moves led to his wife and son being implicated in a plot to assassinate Octavian. More recently, some historians believe he was capable and a good commander, but simply lost to the juggernaut that was Octavian. It should be noted that Antony also lost out to Octavian, and even though he was known as a bit of an idiot with a bully complex, he was no slouch as a military commander.

For a list of ancient sources on Lepidus, see this very helpful guide by Attalus: http://www.attalus.org/names/l/lepidus.html

For Cassius Dio's take on the story: http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Cassius_Dio/48*.html

It should be noted that Cassius Dio was an historian, writing around 200 years after the events. (Caesar assassination in 44 BC, Dio writing around 200-230 CE.) Therefore any propaganda issued by Octavian/Augustus may have coloured his interpretation.