Tomas belongs to the Czech intellectual class, which was silenced after the Soviet invasion of Prague. An internationally known surgeon, Tomas is stripped of his career because he refuses to renounce an anti-Czech Communist article he wrote. This single article puts him in grave danger, although he is not a committed or active political dissident. Ideally, Tomas would like to avoid political parties and society altogether in favor of being a free agent and independent thinker who acts as he chooses. After losing the privilege of practicing medicine, Tomas becomes first a window washer and then a farmer, descending to the lower rungs of society in search of a peaceful life.

As a man, Tomas attempts to practice a philosophy of lightness. He considers sex and love two separate and unrelated entities; he sleeps with many women, and loves one woman (Tereza), and sees no problem with the simultaneous existence of these two ac tivities.

Although Tomas is an intellectual and a thinker, he is no romantic idealist like Simon or Franz. His lover Sabina calls him the "complete opposite of kitsch," or the complete opposite of the shiny, perfect ideals of politics and love. Tomas cannot take seriously the laws on which politics and romantic fidelity are based. His pragmatism, experience, and individualism make him unwilling to identify himself as a political liberal or as a faithful husband. Consequently, most of the characters misi nterpret Tomas; the police and his hospital colleagues think him a dissident, and dissidents think him a coward.

Tomas's character does not fundamentally change over the course of the novel. Instead, Tomas gains a modicum of heaviness. He also grows a little more cynical, as he becomes uncertain of his once firm views on life and being. His love for Tereza and eventual exile to the countryside curb his erotic adventures, but he never necessarily loses the desire for sex with many anonymous partners, or the conviction that such a desire is no crime.