Arcturans

Arcturans are a race of aliens and one of the main antagonists that appeared in the climax of the twenty-third Give Yourself Goosebumps book, Zapped in Space.

Zapped in Space
Upon clearing the Red and Yellow levels of the Vegan's game, the reader and their friends, Katy and Jordan, are transported back into the game room and warned that "The Arcturans are the most intelligent race in the galaxy. No one has ever outwitted them." before being transported to the Blue level. Upon arriving, the three aliens challenge the reader with the three most difficult puzzles that they designed. In order, the puzzles are a Goosebumps trivia question (explained as one of the books being recovered in a time capsule), a magic square math equation, and a space-themed word search where the reader must determine whether an even or odd amount of words can be found.

Upon failing any of these puzzles, the reader and their friends can be sentenced to slave away in the spice mines, become brainwashed into obedient servants of the Arcturans, or disgusting the aliens with your pleading to be sent home, only for them to do so but as a floating head due to lack of spacecraft (in respective order). However, if you succeed in all three puzzles, the Arcturans all explode, too enraged and baffled by the reader's success. Consequently, this leads to the reader and their friends winning the game and liberating the Vegan race in one of the good endings.

Goosebumps (film)
Arcturans appeared in an early draft of the film Goosebumps. An Arcturan, mistakenly referred to as an Acrurien, questions whether or not Slappy should lead all of the monsters.

Physical appearance
Arcturans are described as having big, bald heads that bear resemblance to a human's, but have the stark contrast of pale blue skin. They are kept inside three small, round glass cases and explain their peculiar state to the unnerved reader by saying Arcturans had outgrown the use of bodies as more of their time was spent thinking.

Trivia

 * Arcturus actually happens to exist, being the brightest star in the constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.
 * The back of Zapped in Space calls the aliens Arcturians. However, the species is called Arcturan throughout the book.