The former paratrooper was president of Congo-Brazzaville from 1979 to 1992 under a single-party regime, then returned to office in 1997 after a civil war and has dominated politics ever since.
Dubbed the "emperor," Sassou Nguesso, who is officially 80 and remains fit, is widely expected to run for a fifth term in 2026.
"He makes no secret of it," a diplomat told AFP.
Last September, a rumor of a potential coup spread on social media following a string of coups that have rocked the Sahel since 2020, including Mali, Burkina Faso, Niger and Gabon. But all remained calm in the oil-producing country.
After successive elections in 2002 and 2009, Sassou Nguesso held the presidential reins in 2016 and 2021 by making a constitutional change in 2015 which bypassed the original age limit, 70, and increased the number of five-year terms to three.
'Dinosaur'
Sassou Nguessou may be counted as one of the continent's so-called "dinosaurs," said Thierry Moungalla, government spokesman and communication minister, but he is still in charge.
"The Congolese regime is still here" even though younger regimes have been swept away "by pro-Russian juntas," Moungalla noted.
For Parfait Iloki too, spokesman for the president's Marxist-Leninist turned social democrat Congolese Labour Party (PCT), older age can be a good thing. "It's not a problem, it's wisdom."
"Removing the ruling party has never led to anything," Iloki said.
"By the way, how old is the president of the world's leading power?" he joked, alluding to 81-year-old US president Joe Biden.
But Congo-Brazzaville also recently watched Senegal elect its youngest president yet, Bassirou Diomaye Faye, 44.
"Senegal has a democratic tradition... here, I don't see how a change of this nature could happen," said chaplain Jonas Koudissa, director of the Brazzaville Catholic Academy for Ethics.
For Koudissa, the country's politicians "lack vision" and take advantage of their situation but are not concerned about their country's future.
Tightening the reins
In 2015 demonstrations against a constitutional change led to the government tightening the reins, explained Maixent Animba of the Forum for Governance and Human Rights.
The protests "mobilized a lot of people" and "the regime realized it was hanging on by a thread."
"Overall, we are regressing... in terms of freedom of expression, access to the state media, the right to demonstrate and recognition of parties and NGOs," Animba added citing electoral fraud, misused public funds, privatization and a judiciary "under orders."
"We are not afraid, but we are cautious."
People milling around Brazzaville's streets echoed Animba's caution.
"Here, we're careful what we say, otherwise we'll end up in prison," a taxi driver admitted on condition of anonymity. "Sassou will never leave."
Shopping at Total market, Brazzaville's biggest, 55-year-old Eveline agreed: "We want new blood."
'Where does the money go?'
Shoppers in the muddy aisles of the market all agreed that life is too expensive and difficult, with dire impacts on everyday living.
"One clan has a lot of money, but we don't," added Eveline, a mother herself. "There's no work, our children's diplomas are at home, we can't get medical treatment."
To make matters worse fuel prices have risen in recent months.
The government spokesman explained the increase as the need to answer the International Monetary Funds call for an end to fuel subsidies and a move towards "real prices."
Brazzavillians also deplore the frequent power and water cuts, wondering "where the money is going" from oil.
Opposition leader Pascal Tsaty Mabiala believes the money is being misused, especially on "flashy projects" like the two 30-storey twin towers recently added to the capital's skyline on the right bank of the River Congo.
He added that he thinks Denis Sassou Nguesso will stand for re-election in 2026, faced with an all-powerful PCT and an opposition which is fragmented, muzzled and lacking resources.
"We're a bit tense, as if we lacked confidence in ourselves," the opposition leader regretted.