In the last years of the 19th century and beginning of the 20th, King Leopold II of Belgium ruled the Congo Free State with a tyranny that was peculiarly brutal even by the cruel and deeply racist standards of European colonialism in Africa. He ran the country – now known as the Democratic Republic of Congo – as a personal fiefdom, looting ivory and rubber and murdering millions before the international community stepped in to demand he bequeath the country to the Belgian state.

Yet debate over his legacy has remained muted in Belgium, where hundreds of roads are named after the king along with memorials dedicated to his memory and glory.

Now, under pressure from a growing movement that believes Belgium needs to confront its past, attitudes in the corridors of power are starting to change. As part of a belated reckoning with its colonial history, museums are showcasing sins that were previously overlooked, the tone of history books in school is shifting and, in a development unthinkable until recently, cities have started to remove street signs commemorating Leopold II and openly denounce his legacy.

Facebook Twitter Pinterest Congolese amputees, pictured about 1900. Amputation was frequently used as punishment in the Congo Free State, controlled by Leopold II. Photograph: Universal History Archive/Universal Images Group via Getty Images

The council of Kortrijk, in west Flanders, has said it is renaming its Leopold II Laan [avenue] on the grounds the monarch was a “mass murderer”. Officials in Dendermonde, a Flemish city 20 miles north of Brussels, said they were changing a similarly named street to simply Leopold Laan to avoid further “shame” for residents. Elsewhere, a working group in Ghent is considering the city’s role in Belgium’s colonial past and whether it remains appropriate to have a Leopold II Laan. The mayor of Bruges, Dirk de Fauw, said he was assessing the situation. “If other cities start with it, it could trigger a chain reaction, but there are no plans yet,” he told the Het Nieuwsblad newspaper.

While some municipalities are holding out, the reappraisal offers further evidence of a sea change in how the colonial history is viewed.

Those resistant to change are likely to come under more pressure when a Hollywood film, based on a best-selling book 20 years ago that highlighted Leopold’s bloody rule of the Congo Free State, is released. Last week it was announced Ben Affleck would be producing and directing the film inspired by Adam Hochschild’s King Leopold’s Ghost.

Earlier this year a UN working group concluded in its preliminary report that, nearly six decades after the newly named DRC gained independence from Belgium, many of the country’s institutions remained racist and the state needed to apologise for the sins of its past as a step towards reform. The then prime minister Charles Michel said the government would respond when the UN filed its final report, although he expressed some surprise at the findings. Activists say an important step towards acknowledging the past was made last year when Brussels named a square in honour of Patrice Lumumba, the first prime minister of the DRC, who was assassinated in 1961 with the connivance of the Belgian government. It had taken 10 years of campaigning by the Congolese diaspora and others for the city authority to give its approval. Panels giving information about Leopold II have also been attached to most of his statues in recent years.

Jeroen Robbe, of the anti-racism group the Labo vzw said too many municipal leaders were still failing to show moral leadership: “The fact they are taking this so lightly indicates a blind spot that we have in our own history.

Facebook Twitter Pinterest Inauguration of a square in Brussels, dedicated to the memory of Patrice Lumumba, the first prime minister of the Democratic Republic of Congo, after independence from Belgium. Photograph: Photonews/Photonews via Getty Images

“Not a priority? Nobody would dare say that about a Stalinstraat or a Hitlerstraat. The difference is not the size of the horror, but the skin colour of the victims. You have to change the street names and add an explanation to it, so that we don’t hide away the past.”

In Kortrijk, the council said it was also renaming a street marking the life of Cyriel Verschaeve, a Flemish nationalist priest, and collaborator during the Nazi occupation of Belgium. Alderman Axel Ronse said: “Leopold II was a mass murderer and Cyriel Verschaeve a collaborator. We will support companies and residents who may be affected by the new street names in the future.”