Dr Tan Cheng Bock announced on Friday (Jan 18) that he had taken the first step to forming his new Progress Singapore Party by applying to register it.
Many will remember that he lost narrowly to Dr Tony Tan Keng Yam in the 2011 presidential elections. He was also a long-serving community doctor and active People's Action Party (PAP) MP.
Here are some other facts about the 78-year-old who is making a return to politics.
1. HUMBLE BEGINNINGS
Dr Tan Cheng Bock, the third of six children, had a humble and difficult background.
He studied at Radin Mas Primary School where he recalled being inspired by his school teacher, Mr S. Ratnagopal, to help others.
Tragedy struck when he was 16. His father, a clerk with the Singapore Harbour Board, died suddenly from tuberculosis.
In an August 2011 interview with The Straits Times, Dr Tan recounted that he went to the Singapore Harbour Union where he learnt his family was entitled to a benevolent fund of $28,000.
However, he was told his father had defaulted on union subscription fees and was turned away.
The persistent teenager found a receipt which proved otherwise but the union refused to budge.
Although his father's friends told him not to pursue the matter as the union was very powerful, the Raffles Institution (RI) schoolboy was undeterred.
He sought help from the legal aid bureau and for more than a year, turned up regularly at the union demanding what rightfully belonged to his father.
Meanwhile, he gave tuition, wrote revision books for primary school students and used his bursary to help his family make ends meet.
His persistence paid off and the family got $14,000 - which helped to pay for their first fridge.
He told ST: "It was my first lesson in politics. It takes a lot of stamina, a lot of determination to right a wrong. But you've got to fight if you believe in a cause."
He went on to medical school at the University of Singapore in the 1960s, where he would meet the love of his life: his wife, Madam Lee Choon Lain.
"She was studying pharmacy and I was doing medicine… She also came from a poor family and had to struggle like hell. People like that have an edge lah," he said with a grin.
He recalls with fondness: "When we were courting, she would pester me to stop watching WWF (World Wrestling Federation) and study."
2. A VILLAGE DOCTOR, AND MORE
Before he was a politician, Dr Tan Cheng Bock was a general practitioner. He opened his first clinic - Ama Keng Clinic - in 1971.
At the time, the area in Lim Chu Kang was still a village of attap and zinc roof houses, where villagers grew vegetables in small plots and reared pigs in their backyards.
Dr Tan recalled in a Dec 31, 2018 Facebook post that water came from wells and standpipes and most homes then did not have electricity. He even once delivered a baby in the dim light of a kerosene lamp.
But beyond being a doctor, he also helped fulfil other roles in the community.
"The villagers were simple, honest people - many struggling to make ends meet. So I became more than a doctor, by helping them in family feuds, land disputes and writing letters to government departments," he said.
The village was later uprooted and the villagers scattered in a redevelopment exercise, and its site today is overgrown with vegetation and is now a secondary forest.
"It was extremely traumatic and painful for many, whose only life skill was farming. Countless multi generational households were broken up. They suffered anxiety and depression settling into HDB flats," said Dr Tan.
He later moved into the HDB heartland, where many of his old patients continued to seek him out.
The Straits Times reported last December that Dr Tan would be hanging up his stethoscope after 50 years in medicine.
He told his old patients: "Retirement is not an option for me, I am merely switching my role from serving patients to serving people. I always say that medicine is my love, but politics is my calling."
3. PEOPLE'S ACTION PARTY
Dr Tan may be registering a new party, but this is hardly his first foray into Singapore politics.
A veteran PAP stalwart who served the former single-member Ayer Rajah constituency as MP for 26 years, he has definitely seen his fair share of election battles.
He joined the PAP for the 1980 elections and recalled that the late Mr Lee Kuan Yew interviewed him.
"I left the interview suspecting he was not impressed with me. Moreover, my academic records and CV were colourless. I was only a village doctor with a rebellious streak," he wrote in a Facebook tribute to the founding prime minister in March 2015.
Yet he would serve under Mr Lee for a decade, until Mr Goh Chok Tong took over the reins in 1990.
In his six terms, Dr Tan was regularly among the PAP's top vote-getters, and was the rare backbencher elected to the party's Central Executive Committee, its top decision-making body.
In fact, he won by the widest margin in the 2001 elections - his last contest - with 88 per cent against the Democratic Progressive Party's Tan Lead Shake.
In Parliament, he spoke up against the Government's streaming policies in schools in the 1980s, and also the push for foreign talent in 1999.
In June 1997 and April 2002, he also voted against the Nominated MP scheme.
In 2005, Dr Tan developed meningitis and almost died. He recalled in a August 2011 ST interview that he lost 7kg, staying in a high-dependency ward as he battled the infection.
This prompted him to finally retire from politics in 2006.
He recalled that he sang his favourite song, My Way, at a final post-Budget dinner.
"I changed the lyrics of the song with reference to (an) MP's role. After I sang, (Mr Lee) looked at me and broke into a smile. We then shook hands. To me, it was a good feeling to end my stint as MP for Ayer Rajah," he shared.
He quit the party in May 2011.
4. RUNNING FOR PRESIDENT - TWICE
The presidential election of 2011 was a battle between the four "Tans": Dr Tan Cheng Bock, Dr Tony Tan Keng Yam, former senior civil servant Tan Jee Say and former chief executive of NTUC Income Tan Kin Lian.
It came to a nail-biting race between the first two, with Dr Tan Cheng Bock calling for a recount.
About 738,000 Singaporeans had picked him to be president, meaning he got 34.9 per cent of the vote.
He had also spent the most out of the four candidates on his campaign - $585,045.
In the end, Dr Tony Tan, who had been a Cabinet minister, won - but by a narrow margin of 7,382 votes or 0.34 percentage point.
When asked later about how he felt about coming so close, Dr Tan Cheng Bock told ST in 2016: "To say I was not disappointed is not telling the truth."
While many pundits believed that Mr Tan Jee Say and Mr Tan Kin Lian's splitting of the votes cost him the election, he added that he harboured no resentment towards them.
In March that year, Dr Tan announced his second bid for the nation's highest office, amid a then ongoing review of the elected presidency led by Chief Justice Sundaresh Menon.
His presidential ambitions quickly grinded to a halt, however, when changes were made to ensure that no racial group would be shut out from the presidency.
The Constitutional Commission proposed in September 2016 that if Singapore has not had a president from a particular racial group for five continuous terms, the next presidential election should be reserved for candidates from that group.
The high-level panel also suggested changes to the eligibility criteria.
Dr Tan appealed against the decision to start the count of five terms from the time of President Wee Kim Wee, stating it was unconstitutional.
Eventually, the Supreme Court rejected his final appeal in August 2017, finding the Government's decision constitutional.
But even if the upcoming election were not reserved for Malay candidates, Dr Tan would not have met the criteria of helming a company with $500 million in shareholder equity.
He accepted the verdict with a "heavy heart".
"Nevertheless, I am very comforted to know that many of you were strongly supporting me in this case," he wrote in a Facebook post.
Madam Halimah Yacob was elected, and is the current President of the Republic.
5. KEEPING ACTIVE, MEETING PEOPLE
Even after his failed presidential bid, Dr Tan continued to stay active in current affairs and politics.
Last July, seven opposition parties came together to discuss forming a new coalition, announced by the Singapore Democratic Party (SDP). Dr Tan attended the meeting as an observer.
The others were: the People's Power Party, the Democratic Progressive Party, the Reform Party, the National Solidarity Party, the Singaporeans First Party, and former NSP chief Lim Tean, who applied to form a new party - the People's Voice Party.
SDP secretary-general Chee Soon Juan proposed then that Dr Tan lead the coalition, given his experience and leadership. There was no objection from the others.
At the time, Dr Tan said he would regret it if he had the chance to make a difference, but did nothing.
"I think I must help but in what capacity, I have not decided. I am now 78 years old. I may only have a short time to mentor a team to work for the good of the nation. This is a small window of opportunity... I want to put my last years to good use."
Then in August, Dr Tan gathered his old friends from RI to put together a rendition of a timeless classic, Count On Me, Singapore.
The seven were seen in a video strumming the ukelele as they sang.
Dr Tan said that they hoped to express their love for Singapore through the video.
"It's a timeless song of hope and vision for a better Singapore. May the song speak for your heart as it does for mine," he said in a Facebook post.
Then last November, Dr Tan made headlines when he had Sunday breakfast with Mr Lee Hsien Yang at a hawker centre in West Coast.
Mr Lee, the younger brother of Prime Minister Lee Hsien Loong, said: "We were just here to have breakfast."
Later that morning, Dr Tan said that the two had wanted to catch up with each other as they had not met for a while.
"It was a good breakfast, not only the food, but the sharing we had on world affairs and the current state of politics in Singapore," Dr Tan wrote in a Facebook post.
He also said that several families greeted and even took photos with them.
"We were touched by their warmth and encouragement," he added.