In 2151, the Malurians were secretly mining the Akaali homeworld for veridium isotope using drilling equipment saturated with tetracyanate 622. The mining team was led by Garos, who was disguised as an Akaali shopkeeper most of the time. Most of the other miners were also disguised as Akaali. The entrance to the mine was accessed through a secret passage in Garos' curio shop. (ENT: "Civilization")
In 2267, the Malurian civilization was entirely wiped out by the Earth space probe Nomad. The Malurians were being studied by a Federation science team, under the direction of Doctor Manway, at the time. (TOS: "The Changeling")
The Malurians were originally scripted as the "Tlalokans". A 6 June 1967 review of the "The Changeling" script, by de Forest Research, panned the name "Tlalokan", stating: "Tlaloc is the Aztec god of Rain and Thunder, one of the principal deities in their pantheon. Suggest: Tellians."
The return of the Malurians in "Civilization" was viewed, by Mike Sussman, as an amusing in-joke. "The Malurians are funny," he stated, "because they get wiped out by Nomad a hundred years later [in 'The Changeling'], so it was like, 'Wouldn't it be great to see these guys?' So we made them the bad guys in 'Civilization,' the green lizard guys – they get their comeuppance a hundred years from now!"  In their natural appearance, the Malurians were scripted (in the script of "Civilization") to have "gray, scaly flesh."
In scripted but unused dialogue from "Civilization", Garos – while speaking duplicitously to Starfleet officers from the NX-class starship Enterprise – stated, "My people have very strict protocols when it comes to interfering with other species."