In 1990, Steve Jackson Games published GURPS Aliens, a compendium of Aliens for any sci-fi campaign. What about Traveller? Stat wise, the aliens can of course be used in GURPS Traveller as is, and conversion keys exist for other Traveller rule sets, so that’s not a problem. How to fit the Aliens into the setting of Traveller, however? Here are a couple of suggestions that should work for any published Traveller setting from Classic Traveller on, including the Rebellion, The New Era, The founding of the Third Imperium, or The Rule of Man.

The Markann for Traveller

Everyone knows the stories of giant spider apes that prey on travellers in the dark are just tall tales told by spacers who have been away from civilization a little too long. Everyone is wrong.

The Markann are secretive, high-tech, and insane. In Traveller they are constructs of one of Grandfather’s children, left over from the final war of the Ancients. Very long-lived, they reproduce by cloning. Still their numbers have steadily declined over the many millennia since the destruction of their creator. The Markann inherited the technology of their creator and assumed its role as master and mad scientist. However, they don’t understand the technology. They can operate it and use it to build preprogrammed designs, including themselves, but they cannot reproduce it or extend it.

The Markann dwell largely in hidden bases in asteroids and on moons, though there are a handful of hidden fortress labs on habitable planets. Many facilities house only a single Markann and its slaves. Only one facility retains the ability to build ships. This binds the Markann into a loose culture of dependence and distrust and keeps them from spreading too far. Slaves taken from surrounding settlements and lost spacecraft are trained to keep the facilities and provide stock for the Markann’s horrifying experiments. The Markann mimic their lost creator in trying to reform life, but with a fundamentally flawed theory they resemble the mad scientists of gothic literature and are doomed to perpetual failure. Their offences accomplish nothing.

The Markann have one model of Ancient spacecraft still available. This ship is a spherical spacecraft mounted in a detachable star drive section. The main spherical craft is used for planetary landings while the star drive remains in orbit or hidden elsewhere in a system. The star drive is a ring that fits around the sphere with three long, curved prongs extending both directions. The volume enclosed by the prongs is an ovoid. The prongs spread apart to release the spherical core craft. The ship can also capture small craft between the prongs and transport them bodily in jump space. Almost always only a single Markann is among the crew of a ship.

Markann Adventure Seeds

Monsters from the Dark
At some point in their adventures, when the characters’ ship is crippled in free space, a Markann ship approaches, boards, and takes the crew and passengers back to a hidden base where they become slaves or experimental subjects as suits their aptitudes. The characters must escape. Taking other captives along is optional. Surviving pursuit is mandatory.

Chasing Nightmares
Characters visiting an isolated world are told tales of monsters that snatch people in the night. While they are there, a raid takes place. The Markann grab a macguffin, a person or object, important enough to motivate the characters to pursue. The spherical landing craft has very high acceleration. (It has maneuver drives powerful enough to move the combined ship.) The initial chase is unsuccessful and the characters must quarter nearby systems for a hidden base to retrieve the macguffin.

The Memer and Saret in Traveller

In the Traveller universe, the Memer and Saret are a space faring minor race that does not build jump drives. At the time of contact the Memer and Saret had been space faring in their own system for many thousands of years and were living on every rock bigger than a cobblestone, their existence as a planet bound species only myth. Purchasing jump drive capable ships from humans, large numbers of Memer and Saret (though an unnoticeable fraction of their population) travelled to the stars, not just trading, but also establishing new settlements. Memer and Saret physiology allows them to out compete any other species in settling and exploiting a single star system. In the thousands of years of human contact over empires and interregnums, the Memer and Saret have come to absolutely dominate a significant cluster of star systems. Small human populations exist in Memer and Saret systems.

Trade with the Memer and Saret is very lucrative, but selling them jump capable vessels is a serious, sometimes capital, offence in many systems on the periphery of the space they dominate. The Memer and Saret buy whatever jump capable ships they can. Ships in the worst state of repair are still valuable to them as long as the jump drives work. Thousands of these junker ships ply the star lanes ranging far from Memer and Saret space. Many of these ships are purchased at the extreme limits of Memer and Saret trading routes where the appeal of a quick profit outweighs the fear of an infestation. As traders they are welcome, but viewed with great suspicion. Most human systems do not allow Memer and Saret to settle in any manner.

Memer and Saret Adventure Seeds

Repatriation
A Memer and Saret junker ship has broken down several jumps away from their space. The jump drive is irreparable and the local authorities don’t want the crew hanging around and maybe establishing a permanent presence. The characters’ ship has been hired, or the characters have been hired to crew a ship, to transport the Memer and Saret back to their space while their ship is dropped in the local sun.
The involuntary passengers won’t be any trouble. The whole lot can ride in the cargo bay and they don’t need any life support. They almost certainly won’t interfere with any other cargo or ship systems that pass through the bay. They’ve been asked not to.
Any system en route that doesn’t have a Memer and Saret ship in dock to take the passengers will require the transport to spend as little time in system as possible and have as little contact as possible. Any Memer and Saret ship not heading back to their space will refuse to take the passengers, even if local authorities allowed it, even if the characters can figure out how to ask.
Did anyone think to ask where the Memer and Saret crew came from in the first place?

Delivery
A ship dealer has made a good profit selling a write-off ship to the Memer and Saret. The characters have been hired to deliver the ship to the customer, at a rate that doesn’t cut too deeply into the broker’s profits. The ship is mostly flight worthy—the jump drive works. The route passes through several systems that prohibit the sale of jump drives to the Memer and Saret.

Traveller in a Bottle
The characters have broken their ship in Memer and Saret space. They need to book passage back to a human system on a Memer and Saret ship. This will require them to live in their suits for the trip or rig something else up. The Memer and Saret will accept title to the characters’ ship as payment. The jump drive is probably beyond their ability to repair. The characters will certainly be required to certify on their return to human space that the drive was destroyed beyond repair.
(Alternative: one character travels back to human space to get parts while the rest keep the ship out of alien manipulating appendages.)