The test of a character is simple: describe them to a friend without naming the book. If the friend can repeat it back a week later, the character worked. Plots blur within days — people persist, because readers do not remember events so much as they remember relationships.
Three ingredients do most of the lifting. A want: the concrete thing they are chasing, visible in every scene. A wound: the old injury that explains why the want matters so much, usually installed before page one. And a contradiction: two traits that should not coexist — a gentle person who lies beautifully, a coward who cannot stop volunteering. Contradiction is what makes a person feel observed rather than invented.
Then let them cost you something. A character who never loses never teaches the reader anything. Give them a scene where the contradiction wins at their own expense, and another where it saves them, and you will have written someone your reader will defend in comment sections for years.