Workie, as the animal is called, will star in a TV advertising campaign that starts on Wednesday evening.
Since 2012, 5.4 million workers have been signed up to a workplace pension, under the auto-enrolment programme.
But millions more people who work for small businesses, or individuals, have yet to be offered a pension plan.
All employers are being warned that they need to offer pensions to anyone who is over the age of 22 and who earns more than Â£10,000 a year.
That includes, for example, nannies, care workers, plumbers and bar staff.
The pensions minister, Baroness Altmann, was said to be "personally involved" in designing Workie.
A spokesperson for The Pensions Regulator said Workie was the embodiment of something you cannot ignore.

Shyam Acharya is accused of stealing a doctor's name and qualifications in India before moving to Australia.
He used the credentials to work in local hospitals between 2003 and 2014, New South Wales (NSW) Health said. He also became an Australian citizen.
Mr Acharya was never the individual subject of a complaint.
He is facing a fine of up to A$30,000 (Â£18,600; $18,700) but is likely to have left Australia, said NSW Health Minister Brad Hazzard on Wednesday.
"It is quite disturbing that a foreign national could get through our border protection with a false passport and ID based on an Indian citizen who had trained as a doctor," Mr Hazzard said in a statement.
Local media reported the false identity was that of Sarang Chitale, a doctor who had previously worked in India.
The Australian Health Practitioner Regulation Agency (AHPRA) notified NSW Health it was investigating Mr Acharya in November last year.
He worked at four New South Wales (NSW) public hospitals - two in Sydney, and two on the state's central coast - before his employment ended in 2014.
NSW Health deputy secretary Karen Crawshaw said he was classified as a junior doctor, meaning he was supervised by other practitioners.
Although never the sole target of a complaint, Mr Acharya was part of a clinical team investigated over the treatment of one patient.
Mr Hazzard said he would offer to meet with the patient, who had been told of the alleged deception.
Australian police and immigration officials are investigating how Mr Acharya was awarded citizenship.
"The belief is that he actually trained in a medical course, possibly in India," Mr Hazzard told the Australian Broadcasting Corp.
"Whether he actually completed that qualification is a moot point."
NSW Health said the registration process for doctors had undergone significant changes since 2003.
Mr Hazzard said he would examine "every aspect of registration" to prevent any future breaches.

Hugh Thomson, 67, from Lumsden, drank half a pint of beer and four whiskies, Aberdeen Sheriff Court heard.
Police found that he was more than four times the legal drink drive limit and in breach of a life-long driving ban.
He has been given a community payback order as a direct alternative to jail and a further 10 year driving ban.
The court heard that Thomson, who says he has a terminal illness, was banned from driving for life when he appeared at Fort William Sheriff Court in 1997.
On 23 May this year he drove from Lumsden to Rhynie, a nearby village, and drank in the Gordon Arms Hotel.
People tried to take the car keys from him when he set off for home. He refused to give the keys up and police were alerted, Aberdeen Sheriff Court heard.
Sheriff Alison Stirling imposed a further 10 year ban on driving and told him to carry out 60 hours of unpaid work in the community in a year.
A ten foot tall hairy monster - reminiscent of Sweetums in The Muppets - is to be used to persuade more employers to set up a pension scheme.
[NEXT_CONCEPT]
A man who allegedly masqueraded as a doctor in Australian hospitals for over a decade is believed to have left the country, authorities have said.
[NEXT_CONCEPT]
A man banned from driving for life has appeared in court after he was caught driving his carer's car home from a pub.