Pedro Efraín Alegre Sasiain (born 18 January 1963) is a Paraguayan politician, lawyer, and university professor, who served as president of the Authentic Radical Liberal Party from 2016 to 2023.

[3] For ten years he was the most prominent leader of the opposition to the Colorado Party, running unsuccessfully against its candidates in the presidential elections of 2013, 2018 and 2023.

[6] In 1983, Alegre joined the youth wing of the Authentic Radical Liberal Party (PLRA), belonging in a faction that supported Domingo Laíno.

[12] Public opinion of Alegre during his tenure was positive, with particular praise for the construction of the Avenida Costanera and an aqueduct in Chaco, and additions to Silvio Pettirossi International Airport, as well as his focus on restoring and maintaining Paraguay's architectural heritage.

[16] Two months before the election, Lino Oviedo, the presidential candidate of the National Union of Ethical Citizens, died in a plane crash.

His party, as well as his widow Raquel Marín, released a statement of support for Alegre, describing him as the candidate most likely to achieve Oviedo's hope of preventing a government led by Horacio Cartes.

[17] During his campaign, Alegre called for Paraguay not to return to the past and stressed the need to defeat narcopolitics, which many believed was a reference to Cartes, who was suspected of having ties to illegal organisations.

[19] On 16 June 2016, Alegre was elected as president of the PLRA, defeating Líder Amarilla and Salyn Buzarquis with 38.9% of the vote.

In some areas, polling showed Alegre ahead of the Colorado Party's candidate, Mario Abdo Benítez, in areas including Asunción and departments like Central, Concepción, San Pedro, Cordillera, Guairá, Caaguazú, Caazapá, Itapúa, Misiones, Paraguarí, Alto Paraná, and Amambay.