Don Upatissa Gamanayake (Sinhala: උපතිස්ස ගමනායක; 17 October 1948 – 13 November 1989), also known by his alias Dias Mudalali, was a Sri Lankan politician and the deputy leader of the Jantha Vimukthi Peramuna (JVP) during the 1987–1989 insurrection.

He moved up rapidly in the party hierarchy during the JVP's 1977–1983 democratic phase and became the second in command after the founder and the leader, Rohana Wijeweera.

[2] He was born on 17 October 1948 in Mahingala, Padukka, Sri Lanka as the seventh child in a family with nine siblings.

[4] Gamanayake was married in 1978 to Arambe Devalage S. Karunawathi aka Karuna,[3] a native of Ihalagama, Rambukkana Parape.

He started JVP politics in November 1968 while still in school through Angampodi Cyril Jayaratne, a teacher at Pulmudai Maha Vidyalaya.

Piyasiri Gunaratne, a Trincomalee railway clerk born in Ambalangoda, conducted JVP classes for Gamanayake.

On March 18, 1975, under Wijeweera's guidance, Gamanayake set up a temporary JVP central committee in prison.

[4] Gamanayake and his family lived for some time in a village called Kajugaswatta near the Lenagala Rajamaha Viharaya on Ratnapura Road in Horana.

In his late years, Gamanayake was living in a house about 100 meters down the Model Lane, just south of the Mahawila Junction in Bandaragama, a few miles down Horana Road in Panadura under the name Kuruppuge Gunasiri Dias.

He became popular as 'Dias Mudalali' as he ran a grocery store and a small sewing business in the house called "Nisansala".

[3] Piyadasa Ranasinghe and Somawansa Amarasinghe leave for Madawala in a separate vehicle to retrieve some money that had been kept for security.

On the way back, Somawansa descended Mount Trinity whereas Piyadasa Ranasinghe and H. B. Herath were arrested at Galaha's house on the same day.

[4][3] The biographical film of Rohana Wijeweera's late life titled Ginnen Upan Seethala was released in 2018.

The film was directed by Anurudha Jayasinghe and popular actor Jagath Manuwarna played Gamanayake's role.