Mak Plain was a male banker of the Muun species. He worked for the InterGalactic Banking Clan on Coruscant and Scipio, often acting as a liaison between the Bank and the Galactic Republic.
During the Clone Wars, Mak Plain worked for the InterGalactic Banking Clan, sometimes positioned in his office on Coruscant. In the aftermath of the Confederate–Republic peace initiative, the Galactic Senate began to move forward with the Republic military enhancement bill. It was then that Plain announced a new twenty-five percent interest rate on Republic loans as well as the fact that the Banking Clan would be financing three million battle droids for the Confederacy of Independent Systems. The news infuriated many Senators, including Senator Padmé Amidala.
During an investigation by Senator Amidala into corruption in the Banking Clan, Mak Plain was there to welcome Senator Amidala and her entourage to the planet Scipio. During an intense debate on whether Senator Rush Clovis should be made head of the InterGalatic Banking Clan following the corruption involving the Core Five ruling council, Mak Plain declared that the Muuns endorsed Clovis for the position.
Mak Plain was created for the animated television series Star Wars: The Clone Wars in which he was voiced by actor Stephen Stanton. Plain first appeared in the episode "Pursuit of Peace," which aired on December 3, 2010.