He began his career as a bus driver in Caracas, and then rose through the ranks to become a member of Venezuelan President Hugo Chavez's inner circle.

Now Vice President Nicolas Maduro is the country's interim leader.

Chavez died Tuesday after a long battle with cancer. He had been Venezuela's president since 1999.

Venezuela will hold elections in 30 days and Maduro is assuming the presidency during the interim period, Foreign Minister Elias Jaua told state-run VTV on Tuesday.

Shortly before his last trip to Cuba for cancer surgery, Chavez tapped Maduro as his replacement "if something were to happen that would incapacitate me" and called for voters to support him.

"My firm opinion, as clear as the full moon -- irrevocable, absolute, total -- is ... that you elect Nicolas Maduro as president," Chavez said in early December, waving a copy of the Venezuelan Constitution as he spoke. "I ask this of you from my heart. He is one of the young leaders with the greatest ability to continue, if I cannot."

That televised address marked the first time the Venezuelan president had specified a successor since he announced he had cancer in June 2011.

Maduro, 50, has long been a high-profile face in Chavez's administration.

Serving as both the country's vice president and foreign minister, he often was seen in the front row of Chavez's press conferences and traveled to Cuba many times alongside Chavez as he underwent cancer treatment.

"He is without a doubt one of the ministers who is closest to Chavez," political analyst German Campos told CNN en Español after Chavez tapped Maduro as vice president in October.

As foreign minister, Maduro was the country's top diplomat as ties grew with Cuba and tensions rose with the United States.

In recent years, he has been an outspoken critic of U.S. policies toward Venezuela.

When the Treasury Department added four Venezuelan officials to its drug kingpin list in 2011, Maduro accused the U.S. agency of acting as "a sort of world police agency" that has falsely named "decent citizens of our country ... as drug traffickers."

"A country like that has no moral authority to judge generals and political officials in Venezuela," he said. "We reject it and we believe that the drug trafficking mafias are there, in a sick society like the United States."

After security screeners detained him at New York's John F. Kennedy International Airport in 2006, Maduro called the U.S. government "racist" and "Nazi" and said the United States does not appreciate Latin American countries.

But Maduro doesn't always take an extreme tack, said Javier Corrales, a professor of political science at Amherst College in Massachusetts.

"On the one hand, he has been behind some of the most radical, crazy foreign policy decisions of the Chavez administration. Support for Libya, you name it, all the radical decisions, he has been behind them," Corrales said. "But he also has been behind some of the most pragmatic and conciliatory decisions, including the turnaround in relations with Colombia."

That's a marked contrast with the inflammatory Chavez, who rarely turned to compromise, Corrales said.

Before his role representing Venezuela abroad, Maduro honed his political skills at home.

He became a union leader while working for the Caracas metro system. After Chavez came to power in 1999, Maduro helped draft a new constitution. He served as a congressman until 2006, when he was tapped as foreign minister.