Following are details of the main opposition challengers to Cameroon's 92-year-old President Paul Biya, the world's oldest head of state, seeking to win an October 12 election that could keep him in office until he is nearly 100.

ISSA TCHIROMA BAKARY

A former government spokesperson who most recently served as employment minister, Tchiroma announced in June he was defecting in response to mounting public frustration after more than four decades under 92-year-old Biya.

"A country cannot exist in the service of one man. It must live in the service of its people," Tchiroma wrote in an open letter announcing his candidacy.

That raised the possibility of a realignment in Cameroon's northern regions - Tchiroma's home base - which has traditionally delivered strong support for Biya's Cameroon People's Democratic Movement (CPDM).

Tchiroma is the leader of the Cameroon National Salvation Front, a formerly CPDM-allied party which he founded in 2007, and has previously also served as transport and communication minister.

Though 76 himself, he vowed to be a champion of Cameroon's youth who have long struggled with chronic unemployment.

The current system, Tchiroma said, is incapable of meeting "the demands of a connected, digital and fast-paced world."

BELLO BOUBA MAIGARI

Bouba became the second high-ranking official to announce he would challenge Biya this year, days after Tchiroma, though he did not initially say if he had resigned from his post of tourism minister.

He also hails from the north, intensifying the struggle Biya might face retaining support from a part of the country that, with more than 2.5 million voters, holds significant sway.

Bouba, 78, is a familiar face in government. He was the first prime minister Biya appointed upon becoming president in 1982.

But he also ran to unseat Biya in the country's first multi-party elections in 1992, finishing third with around 20% of the vote.

Two other opposition candidates, Ateki Seta Caxton and Akere Muna, have stepped down to throw their weight behind Bouba.

CABRAL LIBII

Cabral Libii is a former radio presenter and law lecturer who, at 45, is less than half the age of the man he is trying to defeat.

He ran in the 2018 election and finished in third, then rejected the results saying they did not "reflect reality".

Since then he has continued to play up his relative youth, including last year when he attended the inauguration of Senegal's President Bassirou Diomaye Faye, whom he noted is only four days older than him.

He said at the time that, with Faye's win, "a new wind began to blow across Africa and it will cross Cameroon in 2025."

Libii is originally from the Centre region, home to the capital Yaounde.

International Crisis Group describes him as "popular among young people living in Francophone urban areas."

JOSHUA OSIH

Osih, a 56-year-old businessman and lawmaker, took over the leadership of the opposition Social Democratic Front (SDF) party after the demise of its leader John Fru Ndi in 2023.

He has not been keen on the idea of a coalition, arguing that the SDF, which once posed the biggest threat to Biya, can topple him on its own.

The Anglophone parliamentarian has set out a plan to "rescue Cameroon" by 2026, denouncing what he describes as autocracy under Biya.

Central to his platform is a vow to end violence related to the armed separatist conflict in two English-speaking regions within 100 days of taking office.