CHAN CHUN SING
Since his entry to politics in 2011, Mr Chan has developed a reputation for quickly mastering his portfolios and his ability to connect with people on the ground.
Mr Chan's portfolios are significant ones, and complement his time in the Singapore Armed Forces, where he rose to the rank of major-general and was Chief of Army.
He became Acting Minister for Community Development, Youth and Sports in May 2011, a politically important appointment then, given the concerns over rising inequality that the People's Action Party (PAP) had to contend with in that year's general election .
Two years and three months later, he was made full minister, the fastest of his batch to achieve the promotion.
Former Nominated MP Eugene Tan recalls watching Mr Chan in Parliament during the Committee of Supply (COS) debates, the annual Parliament debate over each ministry's Budget. Says Dr Tan: "After one year, he was able to go to COS without referring to his file. That was very impressive."
Mr Chan now holds two important positions: secretary-general of the National Trades Union Congress - that is, labour chief - and People's Association deputy chair.
This means that he has links to two key groups: the trade unions and grassroots organisations.
Within the PAP, he has also been given heavy responsibilities.
Soon after the 2015 general election, he was tapped to head the executive committee of the party's headquarters (HQ), which oversees the administration and coordination of the PAP's activities across its 89 branches. He is also party whip, ensuring the MPs all vote according to the party line so the Government can pass the laws it proposes.
Topping it off, impressively, not to mention important politically, Mr Chan is fluent in three of the four official languages: English, Malay and Mandarin.
HENG SWEE KEAT
To see how far Mr Heng may go, you only have to look at his curriculum vitae (CV) since he entered politics in 2011: In terms of helming heavyweight ministries and national committees, he stands head and shoulders above his colleagues.
He has been the Minister for Education and is now in charge of the Finance Ministry, critical ministries traditionally on the CVs of current and former deputy prime ministers and prime ministers.
In addition, Mr Heng chaired the Our Singapore Conversation national feedback drive in 2013, and the SG50 Jubilee celebrations last year.
He now heads the Committee on the Future Economy, billed as having the key task of transforming Singapore's economy to ready it for the future. PM Lee headed a similar economic committee in 1985.
Mr Heng has some exposure to world leaders and statecraft, having received Chinese President Xi Jinping during his visit here and accompanied PM Lee to the Group of 20 summit in Turkey last November.
And in a sure sign of the Cabinet's confidence in his potential, Mr Heng achieved the rare feat of being made a full minister immediately after being elected as a new MP.
Such a promotion has happened only once before, to former finance minister Richard Hu. Even PM Lee, who entered politics at age 32 in the same 1984 election as Dr Hu, was first appointed as a minister of state.
Before entering politics, Mr Heng started his public service career in the police force and held posts including principal private secretary to then Senior Minister Lee Kuan Yew, and permanent secretary for trade and industry - the highest-ranking civil servant in the Ministry of Trade and Industry.
But a big question mark hangs over his health, given the stroke he suffered in May, says NUS political scientist Reuben Wong. He is said to have recovered well and remains in the running. PM Lee himself had lymphoma - a cancer of the white blood cells - in 1992. It went into remission after chemotherapy, and he became Prime Minister in 2004, 12 years later.
NG CHEE MENG
A newcomer to politics, Mr Ng was given roles in the important ministries of education and transport from the get-go.
A few weeks after both were elected last September, Mr Ng and Mr Ong Ye Kung were both made Acting Minister for Education, splitting the heavyweight ministry between higher education and skills, which went to Mr Ong, and schools, which went to Mr Ng.
The Education Ministry is a closely watched one where future deputy prime ministers or ministers can make their mark.
At the same time, he was also appointed Senior Minister of State for Transport, a hot-button ministry given the high-profile public transport breakdowns in recent years.
The appointments may be PM Lee's way of rounding out Mr Ng's strong military experience, giving him more and deeper exposure to the business of government. After all, before Mr Ng entered politics last year, he had risen to the apex of the armed forces as lieutenant-general and Singapore's Chief of Defence Force.
Rounding out his military experience, he was also on the boards of several public organisations such as the Defence Science and Technology Agency and JTC Corporation.
ONG YE KUNG
Mr Ong joined the Cabinet one electoral cycle later than intended, having been part of the defeated People's Action Party team in Aljunied GRC in 2011.
But he seems to have turned that defeat into resilience, returning to politics at the general election last year. His strength vis-a-vis the others is his diverse range of experiences, given his years in the labour movement and the civil service.
Furthermore, between 2013 and last year, he worked in Keppel Corporation as director of group strategy, making him the only contender with corporate experience - a valuable different perspective.
But first, he earned his stripes in the civil service. Mr Ong worked closely with PM Lee as his press secretary and then principal private secretary, was the deputy chief negotiator for the US-Singapore Free Trade Agreement, and was chief executive of the Singapore Workforce Development Agency. He then joined the labour movement, rising to be deputy secretary-general.
Now the Acting Minister for Education (Higher Education and Skills), Mr Ong is in charge of universities, polytechnics, the Institute of Technical Education and SkillsFuture, all at the forefront of the Government's drive to get Singaporeans to upgrade themselves with relevant job skills.
He is also Senior Minister of State for Defence, and was recently appointed to the Monetary Authority of Singapore (MAS) board of directors, rounding out his experience in finance. Whether he can make up for lost time should be clearer come a mid-term Cabinet reshuffle.
Touted as a part of the core of the fourth-generation Cabinet, Mr Tan had a bit of a rocky start but has since settled well into his current role as Social and Family Development Minister.
He was appointed the Acting Manpower Minister in August 2012 and made full minister two years later.
However, in August 2013, Mr Tan was asked to relinquish his second portfolio as Senior Minister of State for National Development, which raised questions at the time about his prospects. PM Lee said he wanted Mr Tan to drop his Ministry of National Development role so he could concentrate on helming the Manpower Ministry.
He proved himself, and a year later at the August 2014 Cabinet reshuffle, PM Lee said Mr Tan had performed well since taking office and had mastered his portfolio.
Mr Tan then succeeded Mr Chan as Minister for Social and Family Development in the April Cabinet changes last year. He was also the anchor minister for the PAP's team in Marine Parade GRC.
However, in February last year, he was diagnosed with pleural tuberculosis, a rare form of the disease which infected the area between his lungs and rib cage. He made a full recovery last October.
As a brigadier-general in the Singapore Armed Forces, Mr Tan led humanitarian relief efforts in Aceh after the 2004 tsunami, Singapore's largest military operation to date.
Mr Wong, the Cabinet's youngest minister at 43, has stepped up to bigger roles recently, having been assigned roles in two challenging ministries.
He was initially made Acting Minister for Culture, Community and Youth in November 2012, and was promoted to full minister later in May 2014. He was also Second Minister for Communications and Information from May 2014 up till October last year, when he was appointed National Development Minister.
He oversees much of the national infrastructure, including the important matter of public housing, which more than four in five Singaporeans live in.
He was previously a high flier in the civil service, having worked closely with PM Lee as his principal private secretary before moving on to head the Energy Market Authority. Mr Wong also has experience in finance matters, having sat on the board of the Monetary Authority of Singapore.
He was appointed Second Minister for Finance to assist Mr Heng last month, on top of his National Development portfolio.