Guilherme Posser da Costa is a São Toméan who served as the ninth prime minister of São Tomé and Príncipe from 1999 to 2001.

Presidential elections were held in São Tomé and Príncipe on 18 July 2021. As no presidential candidate received a majority of the vote, a second round was originally scheduled to be held on 8 August 2021. However, following an objection to the first-round result, the second round was postponed to 29 August 2021, and later postponed again to 5 September 2021.