There are a variety of characters throughout the trilogy. A majority of them only appear for one novel, however. Below is a list of characters that have been featured throughout the series.
Cam - Belly's first boyfriend and summer fling. He is kind, awkward and morally upright. He is a bit of a book nerd, preferring to study and focus on his academics than attend parties. He only appears in The Summer I Turned Pretty.
Anika Johnson - She is one of Belly's college roommates, with the two meeting at a party when playing Never Have I Ever. She and Belly become very close friends and have a sisterly relationship, even more so than Taylor. She only appears in We'll Always Have Summer.
Jillian Capel - Belly's first college roommate. She is different from Belly in the sense that she is more serious about her school studies and has a high preference to be clean and organized as opposed to Belly. However, the two get along with each other. She only appears in We'll Always Have Summer.
Ernie - An elderly widow Conrad visits on a frequent basis. He advises Conrad to stop Belly from marrying Jeremiah and confess his feelings for her before it's too late, being able to tell how Conrad felt based on his own experience with love. He only appears in We'll Always Have Summer.