The portal aliens were aliens who made use of a time portal for recycling in a cave on the unknown planet. They were tall, hooded figures with bright, glowing goggles.
After they caught Will Robinson and his sister Penny using their portal, they transported them aboard one of their spaceships along with the Robot. They explained that generations ago they faced a disaster on their planet and used the energy of their star to build a vast network across the galaxy. They use the unknown planet because it has long been abandoned and they did not expect anyone to be on it. Will and Penny beg them to let them go, but they fear that due to their emotional nature, they will use the portal again, it being too great a temptation. They offer them the choice of either being placed in an alien zoo, or being killed. Will, however, told the Robot to "be... bad" and had it attack the aliens. The Robot then transported Will back to a moment before he had ever interacted with the portal, preventing the sequence of events from occurring.
Trivia[]
The portal aliens appear in the book Lost in Space: Return to Yesterday. It is hinted that they will likely appear in future stories. It may be non canon