We're talking about fiction here. There are three kinds of novels: character driven, plot driven, and character/plot driven. Character-driven or "mainstream" novels often have plots, but they are secondary - the emphasis is on the development of the characters. In this type of novel, the character often comes first. You create an interesting character and throw them into an interesting situation, and see what they do.
A plot driven novel (sometimes called a "thriller") includes the various genres: scifi, fantasy, mysteries, romance, horror, etc. The characters could be anyone, it's the events in the story that are important. Alice in Wonderland, The Wizard of Oz, etc. are good examples. Alice could jump into Oz and Dorothy into Wonderland and nothing would change. Alice and Dorothy are purposely not developed as characters so that they represent "everyperson" - making it easier for a wide range of readers to identify with them.
In the third type, the character/plot driven novel, we find many of our best books. The plots are often unique and exciting (LOTR) and the characters well-developed. These are the novels that win Pulitzer prizes and sell well over the years, are read at school, etc.
Some writers resist stuffing their work into categories; this is mostly for the benefit of publishers, who must separate books to accommodate the many readers who read only romance, only scifi, etc.