from what I understand, most of the voice acting was dun in house by members of the development team. Even duke Nukem was at one point voiced by someone with direct ties to the project (in this case, Marketing executive Joe Seagler). there were fiew exceptions, like the star wars and indiana joens arcade games using voice clips from the source material or Michael Ri narrating the attract modes of Don Blooth's laserdisk games.
the closest thing we got to a professional voice actor in a non licence based, non laserdisk game was indipendent Film director Earny Fasilios as the iconic dungian master in gauntlet 1 and 2.
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