Only 9 percent of Britons named Charles as one of their favorite royals, according to an Ipsos MORI poll released Monday. That's down from 21 percent in 2012.
That's certainly not the case for his sons. Harry is the most liked royal, notching 42 percent of the people asked, with Prince William not too far behind at 30 percent.
Upcoming big family celebrations, including his 70th birthday on Nov. 14, could help soften Charles' image just as he's increasing his royal duties and standing in for his mother, Queen Elizabeth II, more often.
The 20th anniversary of Princess Diana's death last summer may have contributed to Charles' low popularity ratings. Decades-old videos of Diana speaking emotionally about her then-husband's affair with his former girlfriend and current wife, Camilla, reminded Brits of the painful and very public breakdown of their marriage.
"He's always been viewed in context of his family," said Carolyn Harris, a royal historian and the author of "Raising Royalty: 1000 Years of Royal Parenting."
"He's overshadowed by the queen, and during his marriage to Diana she was the more famous half of couple," Harris said. "Now we see him in the context of his relationship with his sons and grandchildren."
“Some of the predictions he made 20 years ago when he started talking about climate change, bad architecture and organic farming… have now been proved to be true.”
That was certainly the case after the birth of Prince Louis when the press focused on why Charles didn't see his grandson in the days after the birth.
Charles has acknowledged that he doesn't always manage to connect with the public. In an interview carried out by Harry, broadcast on the BBC in December, Charles gave the example of his warnings on the environment, which he said were initially ignored.
"There's a whole lot of things I've tried to focus on over all these years that I felt needed attention. Not everybody else did," he said. "But maybe now some years later they are beginning to realize that what I've been trying to say is not as dotty as they thought."
Charles is the longest-serving heir apparent, who are traditionally given the title Prince of Wales. By contrast, his mother, Elizabeth, was only 25 when her father died and she became queen, giving her little time to make a mark outside the role of monarch.
With an official job description of "heir to the throne," he has had relative freedom in creating his role. Charity has become his life's work and he's closely involved with more than a dozen organizations and foundations he started, which operate under the banner of the Prince's Charities.
These causes include helping young people in their careers, improving teacher training and regenerating economically depressed areas. Charles also champions global sustainability.
The oldest and largest of his charities, the Prince's Trust, has helped more than 870,000 disadvantaged young people over the years, according to the organization. It offers access to educational programs as well as loans, grants and support to start their own enterprises. Charles founded it 40 years ago with his navy severance pay of $10,000.
In the past 10 years, the charities have raised more than 1 billion pounds (around $1.4 billion in today's dollars), according to palace officials who didn't elaborate on how the money was raised. They declined to say how much money Charles has personally donated from his fortune to charitable work.
Last year, Charles' income from the Duchy of Cornwall, created in the 14th century for the benefit of the Prince of Wales, was $28.1 million, according to its annual review. He also received $1.7 million from the queen's government allowance, known as the Sovereign Grant. The money is spent on personal and official expenses for both him and Camilla, as well as his sons and their households.
Charles' charity work, however, has not helped him shed a reputation for being pampered and out of touch with ordinary life. During an April trip to Australia, a local radio reporter asked him about longstanding rumors that he travels with his own toilet seat.
"Oh, don't believe all that crap," the prince responded.
In addition, his passion for the various causes he supports has opened him up to criticism that he has ignored restrictions on a monarch's involvement in politics. Although the strictures on the queen to stay out of politics don't officially apply to the Prince of Wales, the British public is sensitive to any appearance of royal meddling.
In a series of letters written in 2004 and 2005, and published in 2015 by The Guardian newspaper, Charles voiced his opinions about top members of the government, including the prime minister. Nicknamed the "black spider memos" after his handwriting, the letters show Charles advocating issues ranging from reducing red tape for farmers to the preservation of historic huts in the Antarctic.
The content was less important than the fact that the prince was offering his opinion, and he was sharply criticized in the press for political lobbying.
"Once he is the monarch, Prince Charles will play a central role in lawmaking, but the idea in the modern day is that the role should be formal," said Thomas Adams, an associate professor of law at Oxford University. "So, when you see him in the time in the lead-up to the role trying to exercise political influence, people get worried."
Charles has also been criticized for supporting homeopathy, an alternative medical treatment that isn't considered scientifically valid by the medical community.
Still, as Charles approaches 70 — an age when many would start to slow down — he remains one of the busiest royals. He holds hundreds of official engagements each year, both at home and overseas, where he serves as the queen's representative now that she's cut back on foreign travel.
The palace regularly publishes videos and photos on social media of Charles and Camilla during their royal trips and engagements. On his trip to Australia in April, Charles quipped to a didgeridoo master that he "felt better already" after receiving a traditional blessing.
When Charles does eventually becomes king after the death of Queen Elizabeth II, his reign will be far shorter than his mother's, who with 66 years on the throne is Britain's longest-reigning monarch.
But he has had plenty of time to prepare.
"Some of the predictions he made 20 years ago when he started talking about climate change, bad architecture and organic farming … have now been proved to be true," NBC royal expert Camilla Tominey said.
"And actually the sustainable, environmentally friendly prince is very much of the 21st-century mold."