Lavamen are a type of sentient being which inhabit Mars.
Little is known about Lavamen. They live near the volcanos of Mars. They have been mentioned several times in Sparks Nevada, Marshal on Mars, but not directly encountered in an episode.
It is mentioned that they are impervious to lava or being burned by Lava. They also hibernate.
In "She Blinded me with Technology", Sparks Nevada mentions that once he saved Croach from some Lavamen, then later that day Croach saved Sparks from some different Lavamen. The onuses were fine that day.