stylistic:style_transfer
Minister Mentor (2004–2011)

In December 2004, Lee stepped down to become Minister Mentor. Expressing concern about the declining proficiency of Mandarin among younger Chinese Singaporeans, he started a year-long campaign called " 华语 Cool! " (Mandarin is Cool!) to garner interest in using Mandarin.

On 13 September 2008, Lee underwent treatment for abnormal heart rhythm (atrial flutter) at Singapore General Hospital. The treatment was successful, and he was well enough to address a philanthropy forum via video link from the hospital. On 28 September 2010, he was hospitalised for a chest infection, cancelling plans to attend the wake of the Senior Minister of State for Foreign Affairs, Balaji Sadasivan.

In November 2010, Lee's private conversations with James Steinberg, US Deputy Secretary of State, on 30 May 2009 were among the leaked US Embassy cables. In a US Embassy report classified as "Secret", Lee gave his assessment of a number of Asian leaders and views on political developments in North Asia, including implications for nuclear proliferation.

In January 2011, the Straits Times Press published the book Lee Kuan Yew: Hard Truths To Keep Singapore Going. Targeted at younger Singaporeans, it was based on 16 interviews with Lee by seven local journalists in 2008–2009. The first print run of 45,000 copies sold out in less than a month after it was launched in January 2011. Another batch of 55,000 copies was made available shortly after.

After the 2011 general elections in which the Workers' Party, a major opposition political party in Singapore, made unprecedented gains by winning a Group Representation Constituency (GRC), Lee announced that he decided to leave the Cabinet for the Prime Minister, Lee Hsien Loong, and his team to have a clean slate. Some analysts, such as Citigroup economist Kit Wei Zheng, believed that the senior Lee had contributed to the PAP's poor performance. In particular, he stated during campaigning that the voters of Aljunied constituency had "five years to live and repent" if they elected the Workers' Party, which some viewed as having backfired for the PAP as the opposition went on to win Aljunied.

In a column in the Sunday Times on 6 November 2011, Lee's daughter, Lee Wei Ling, revealed that her father had peripheral neuropathy. In the column, she recounted how she first noticed her father's ailments when she accompanied him to meet the former US Secretary of State Henry Kissinger in Connecticut in October 2009. Wei Ling, a neurologist, "did a few simple neurological tests and decided the nerves to his legs were not working as they should". A day later, when interviewed at a constituency tree-planting event, Lee stated: "I have no doubt at all that this has not affected my mind, my will nor my resolve" and that "people in wheel chairs can make a contribution. I've still got two legs, I will make a contribution".