Most Stable Diffusion checkpoints have a rough idea of what doomguy looks like. But they mix all versions and variations together. This LoRA was trained on 30 fanarts of the classic doomguy from the 1993 Doom video game. It should works on most SD 1.5 checkpoints.
Check the model page or CIvitai for a list of artists whose work has been used to train this LoRA. https://civitai.com/models/59853/classic-doomguy
