Lysis is a figure from Classical Athens in the late 5th century BCE, known exclusively as a character in a philosophical dialogue by Plato. He is presented as a young Athenian boy, the son of Democrates, and a friend of another youth named Menexenus. The dialogue named after him, Lysis, is set around 409 BCE and features Lysis and his friend in conversation with Socrates.

Lysis is not historically attested as an author or philosopher. His entire significance lies within Plato’s work, where he serves as an interlocutor. The dialogue uses his character to explore the nature of friendship, or philia, examining whether it is based on similarity, opposition, or the pursuit of the good. According to modern scholars, the Lysis is an important early Platonic text for the study of ethics and personal relationships.

No writings are attributed to a historical person named Lysis. The sources confirm he is a literary character created by Plato for philosophical discussion, with no evidence of independent works or a separate philosophical tradition.