A towering cuboid made of more than 300 masks depicting the faces of transgender and non-binary people, this year’s fourth plinth artwork, has been described as a piece designed to “unite the trans community around the world”. The Mexican artist Teresa Margolles was flanked by members of her country’s trans community as Mil Veces un Instante (A Thousand Times in an Instant) was unwrapped in Trafalgar Square on Wednesday. Margolles said in a statement that the work, which is the 15th to stand on the plinth in the London square and features “life masks” of 726 people (363 each from Mexico and the UK), was a tribute to Karla La Borrada, a 67-year-old trans singer and former sex worker who was murdered in Ciudad Juárez nine years ago. Margolles said: “We pay this tribute to her and all the other people who were killed for reasons of hate. But, above all, to those who live on, to the new generations who will defend the power to freely choose to live with dignity.” Ekow Eshun, the chair of the fourth plinth commissioning group, said the piece could help “unite the trans community around the world” and that it was one of the most “nuanced” and “timely” artworks to sit in the space since the project started in 1999. Margolles won the commission for the fourth plinth in 2021, alongside a sculpture by Samson Kambalu, which stood in the square last year and was a comment on the legacy of colonialism in Africa. Each of the masks that make up Mil Veces un Instante has a name and features traces of the person on whom it was based, with lipstick smears and false eyelashes visible on the work. The unveiling of the plinth is a big moment in the UK’s arts calendar and since it began in 1999 with Mark Wallinger’s Ecce Homo it has divided opinion, with some politicians calling for the space to be occupied by a statue of the queen instead. Last year, the former plinth artist Rachel Whiteread called for the project to be scrapped after a Guardian investigation revealed only one of the winning commissions was on display in the UK, while three-quarters of the former fourth plinth works were locked away in storage. She said: “I think it has run out. There have been some really great projects and then there have been some that are not so great.” However, with backing from the London mayor, Sadiq Khan, and under the stewardship of Eshun, the commission has evolved into an international competition that draws as much attention as any other British art prize. Most of the first 15 plinth commissions were given to UK artists, but the next two winners, Tschabalala Self and Andra Ursuța, who were announced in March, are both international artists, meaning that since 2022 all of the winners have come from abroad. Margolles told the Guardian earlier this month that she was not worried about the masks decomposing during their two-year slot, during which they will be exposed to London’s inclement weather. She said: “They will fade and transform … each cast will react to the elements in its own way, according to the organic materials left on the mask.” Margolles has said her plinth commission was inspired by the Mesoamerican tradition of tzompantli, in which storage units were used to display the skulls of sacrifice victims or prisoners of war. Eshun was joined at the unveiling by Justine Simons, the deputy mayor for culture and the creative industries, who said the UK’s public statues did not mirror the diversity of the country, and especially a city like London. She said: “Today we are changing that story. This collective portrait of the trans community is a celebration and an act of solidarity with those who do not enjoy the same freedoms as we enjoy in the UK.”