Who is Archie in Stargirl? Why do the kids enjoy spending time with him

Archie, or Archibald Hapwood Brubaker, to give him his full name, is an old man who lives in the neighborhood near to Mica Area High School. He's a retired paleontologist, someone who uses fossils to study the history of life on earth. A widower, he moved to Arizona after his wife passed away and brought his extensive collection of fossils and bones with him. Archie lives alone, although he has an enormous cactus in his backyard called Señor Saguaro to keep him company and with whom he likes to talk things over.
Archie's very popular with the neighborhood kids because he teaches them all kinds of interesting stuff. He even forms them into an informal group called the Loyal Order of the Stone Bone, which meets up regularly at his place. As Archie tells the kids, his school's always in session. The kids don't just learn about academic subjects at Archie's place; they also receive sage advice concerning Stargirl. When Leo and Kevin ask Archie about this strange new girl in class, he tells them that they should pay attention to her. This way they might actually begin to understand her better.