The Bedford Glossary of Critical and Literary Terms - Ross Murfin 2018
Flat and round characters
Flat and round characters: Terms coined by English writer E. M. Forster in Aspects of the Novel (1927) to refer to the depth and complexity of characterization. Flat characters lack depth and complexity. They tend to be caricatures defined by a single idea or quality whose essences can be summed up in a sentence. Round characters, by contrast, are fully developed, with the complexity and depth associated with real people. They can surprise readers convincingly, for they have full-blown personalities complete with contradictions and quirks that make it difficult to describe them reductively. Forster argued that a mixture of flat and round characters is needed in order to represent the world as readers perceive it, so he did not automatically assign a pejorative connotation to flat characters.
EXAMPLE: Of the two adolescent major characters in the early volumes of George R. R. Martin’s fantasy series A Song of Ice and Fire (1996; adapted to television as Game of Thrones [2011— ]), the predictably obnoxious, cowardly, and cruel Joffrey Baratheon is as flat as his understated, brave, and resourceful counterpart Arya Stark is round.