A burly former bus driver who rose through leftist political activism to become Venezuela's top diplomat will be a key player as the vice presidential pick of President Hugo Chavez, who is heading into a new six-year term after a year of cancer treatment.

Nicolas Maduro has shown unflagging loyalty and become a leading spokesman for the socialist Chavez as foreign minister. His appointment as vice president had been widely expected.

Chavez named Maduro as his choice Wednesday, three days after winning re-election, and the announcement renewed speculation about whether the 58-year-old president could finally be grooming a successor in case his health worsens.

Since being named foreign minister in 2006, the mustachioed, 49-year-old Maduro has overseen many key international efforts, including consolidating the regional diplomatic blocs ALBA and Unasur, strengthening relations with countries including Russia, Iran and China, and achieving a rapprochement with U.S.-allied Colombia.

"He has been Chavez's best spokesperson. He appears strong, he's charismatic to some, and he is loyal," Eduardo Gamarra, a Latin American studies professor at Florida International University in Miami, said Thursday.

The vice presidential job has assumed new importance because of Chavez's recent struggle with cancer. After a year of treatment that included surgeries, chemotherapy and radiation treatment, Chavez said in June that tests showed he was cancer-free. He has said tumors were removed from his pelvic area but hasn't specified the exact location or type of cancer.

During Chavez's visits to Cuba for treatment, Maduro was among the few aides seen at his side, and that presence encouraged speculation he could fill in for Chavez if necessary. During one televised appearance in Cuba in April, Maduro was shown on television playing bocce ball with Chavez and the president's elder brother, Adan.

Maduro is an influential leader within Chavez's United Socialist Party, and before becoming foreign minister was National Assembly president.

David Smilde, a sociology professor at the University of Georgia who studies Venezuela, said Maduro's appointment is significant and shows the type of leadership Chavez wants to emphasize.

"He is among the true leftists in the Chavez government. He believes in state control of the economy, anti-imperialist foreign policy, and the predominance of the executive over other branches and levels of the government," Smilde said.

"My guess is that making Maduro VP has a lot to do with Chavez's health," Smilde said. "As a potential successor to Chavez, Maduro is someone who would continue with the leftist elements of Chavez's project, keep the base happy, continue close relations with Cuba, but perhaps be more comfortable in political negotiations than other potential successors or Chavez himself."

Some observers consider Maduro to be the official within Chavez's inner circle with the closest links to Cuban leader Raul Castro, his brother Fidel and the island's government.

Chavez's close friendship with Maduro goes back to the 1980s, when the Venezuelan leader was an army officer and formed a clandestine movement that eventually carried out a failed 1992 coup attempt.

In his youth, Maduro belonged to a small political group called the Socialist League and traveled to Cuba for training in union organizing. He became a union organizer when he was working as a bus driver in Caracas.

"Look where Nicolas is going, the bus driver," Chavez quipped as he announced the appointment as vice president. Maduro smiled in the audience as the president said: "Look how they've mocked him. The bourgeoisie makes fun."

Chavez regularly chides many of his government ministers during televised meeting, questioning them about perceived mistakes or unfinished projects. But Chavez always speaks affectionately of Maduro.

Chavez sometimes jokes that Maduro eats excessively, saying he should cut back on the submarine sandwiches he likes to devour.

Maduro has proven adept at speaking on Chavez's behalf without getting ahead of his boss' public statements. Still, like most of Chavez's aides, Maduro doesn't stand out as an orator and usually keeps his public statements short and to the point.

As vice president, he replaces Elias Jaua, who is running for a state gubernatorial seat in Dec. 16 elections against Henrique Capriles, the opposition candidate Chavez defeated in the presidential race.

During Chavez's nearly 14-year-old presidency, he hasn't anointed any clear successors, and has rotated various allies through the vice president position. Maduro is his eighth vice president.

"The interesting thing to watch now will be whether Maduro takes on more responsibility than his predecessors and gets involved in a more substantive way in government business, which would be a sign that Chavez is indeed grooming him as his successor," said Nicholas Watson, a Bogota-based analyst for the consulting firm Control Risks, headquartered in London.

It's possible Chavez waited to announce his vice presidential choice until after winning re-election because doing so sooner "could have triggered internal divisions within the ruling party," said Diego Moya-Ocampos, an analyst with the consulting firm IHS Global Insight in London.

Moya-Ocampos said that within Chavez's movement, where civilian and military-aligned wings coexist, Maduro may be a "more conciliatory figure" than Jaua. Coordination with regional party leaders will likely be important ahead of the December elections and as Chavez looks to encourage more community decision-making through "communal" councils and other local bodies, he said.

Maduro's role also could vary significantly depending on Chavez's health, and provided his illness doesn't recur Maduro is likely to act mainly as the president's "close aide and negotiator," Moya-Ocampos said.

Political analyst Ricardo Rios said he thinks Maduro, as the political chief of the civilian wing of Chavez's party, was chosen in part to achieve a balance between different blocs and dole out allowances of power.

He noted that Diosdado Cabello, the president of the National Assembly and a former military officer, is another prominent party leader who will remain in an important national role rather than being assigned to run for a state governor's office.

Maduro knows well how the government works and can help further Chavez's larger goals as he plans to start a "new phase" in his Bolivarian Revolution movement, said Vladimir Villegas, a journalist and former Venezuelan diplomat. He said Maduro carries weight due to his political acumen, experience as a union leader and the international profile he built working with allied countries.

With his re-election win in hand, Chavez says he will deepen his socialist policies in his new term. He first took office in 1999 and now has the ability to complete two decades in office — as long as his health holds.