@sambear You’re right that the material is a Blender Internal material in the file which isn’t directly compatible with Cycles. But to re-create the material for Cycles is very easy.
- Switch your render engine to Cycles
- Go to the material panel and press “Use Nodes”
- In the node editor you should have a principled BSDF node plugged into a Material Output Node.
- Add an image texture node and select the “melvin_diffuse” image.
- Plug the color output into the base color socket of the Principled BSDF
