He was 77.

Officials did not disclose a cause of death. But Sata had traveled to London for unspecified medical treatment last week.

He died in a hospital there Tuesday evening, the government-owned Zambia Daily Mail said.

Sata took office in September 2011 after the incumbent President tearfully conceded in a televised speech, a rare moment in a continent known for volatile elections and leaders fighting their defeat tooth-and-nail.

Analysts hailed his election as an example of an African nation with a vibrant democracy. But not too long after he took office, speculation swirled over his lack of visibility — which especially stood out for a man who loves the spotlight.

Aides said his absence was a result of private international visits, and maintained those trips had nothing to do with medical treatment.

The nation's bloggers have frequently criticized what they describe as "absence of leadership," leading him to make a surprise appearance in parliament last month and declare that he was not dead.

Sata was born in the Zambian town of Mpika in 1936, and worked as police officer during the colonial administration. He later trained as a pilot in Russia before returning home and helping develop housing projects in the nation.

During Zambia's struggle for independence from Britain, he jumped into politics, and later founded the Patriotic Front — then an opposition party. His campaign events electrified crowds drawn to his extroverted nature and fight for the average man.

Sata, who narrowly lost to his predecessor Rupiah Banda in 2008, was a major critic of Chinese investment in the nation's copper industry. He especially targeted foreign companies that mistreat Zambian workers, making him popular among the nation's miners who accused the Chinese of deplorable work conditions.

While in office, he warned foreign companies that while their investment is crucial to his nation, they must abide by the labor laws.

The veteran politician has served in other positions, including city council, member of parliament and cabinet minister for local government.

Before his election, the tiny, copper-rich nation in southern Africa had been ruled by the same party for decades.