He is one of the most powerful leaders of the Venezuelan government, a hard-liner who has put down protests, confronted rebels and been a constant presence at the side of Nicolás Maduro, the country’s authoritarian president.

But for years, Tareck El Aissami, one of Mr. Maduro’s closest confidants, has also been the target of wide-ranging investigations by his own country’s intelligence agency into his ties to the criminal underworld.

According to a secret dossier compiled by Venezuelan agents, Mr. El Aissami and his family have helped sneak Hezbollah militants into the country, gone into business with a drug lord and shielded 140 tons of chemicals believed to be used for cocaine production — helping make him a rich man as his country has spiraled into disarray.

With its economy in tatters and its people hungry, Venezuela is in the throes of a desperate fight for control of the country. Opposition leaders are calling for an uprising, while the country’s military and civilian authorities are refusing to surrender power, presenting a largely united show of force against the protests in the streets.