Lord Tim Bell, the co-founder of Bell Pottinger, has died aged 77 after a long illness, UK media reported on Monday.
Bell, who was at the helm of the PR company for three decades, had left the firm by the time it collapsed in September 2017. He exited in August 2016.
The London-based firm faced heavy criticism following a controversial contract for the Gupta family that included stoking racial tensions in South Africa. It was ultimately expelled from the UK's Public Relations and Communications Association (PRCA) before finally going into administration after its other clients fled.
Its other controversial clients included former SA president FW de Klerk, Asma al-Assad, the wife of Syrian president Bashir al-Assad, and athlete Oscar Pistorius.
Bell was also an advisor to Hernán Büchi, a finance minister in the Pinochet dictatorship, as well as acting as an advisor to friends of poisoned former KGB officer Alexander Litvinenko, according to the Guardian newspaper.
He was hailed as a key factor in the election triumph of former UK prime minister Margaret Thatcher in 1979, after he coined the famous "Labour isn't working" slogan, the Financial Times and other media reported. Thatcher subsequently knighted him and he was awarded peerage by Tony Blair.
The PRCA said in a statement on Monday: "It is with great sadness that the PRCA today learnt of the passing of Tim Bell."
PRCA Director General Francis Ingham added: "Of all those who can be said to have made the modern PR and communications industry, Tim Bell stood preeminent, an undisputed giant who proved the power of communication.
"Nobody can question he was controversial, and indeed he delighted in being so. But nobody can question his greatness either."