The Sophist is one of a small number of late Platonic dialogues in which Socrates cedes the lead role, in this case to the Eleatic Stranger, a follower of the presocratic philosophers Parmenides and Zeno. The discussion is presented as taking place a few days after the Theaetetus, and picks up some of the earlier dialogues themes in the course of discussing how the sophist differs from the true philosopher and the statesman.
Free Online and Downloadable Texts
Gutenberg: The Sophist, translated by Benjamin Jowett, multiple formats.
University of Adelaide (Internet Archive): The Sophist, translated by Benjamin Jowett. EPUB, HTML and MOBI formats.
Wikisource: The Sophist, translated by Benjamin Jowett. Online text.
History of Philosophy without any gaps: Fiona Leigh on Plato's Sophist - podcast by philosophers Peter Adamson and Fiona Leigh.
Librivox: The Sophist - audiobook.
PhilPapers: Plato - Sophist - bibliography with open access option.
Stanford Encyclopedia of Philosophy: Method and Metaphysics in Plato's Sophist and Statesman.
Wikipedia: The Sophist.
The Great Conversation: Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: Plato's Dialogues are listed.