Josef K. is a rather arrogant, haughty, and ambitious man—though he's fairly ordinary. He lives in a lodging house where one day he is arrested. He tries, hopelessly, to get a fair trial and prove his innocence. That is impossible in the novel's absurdist reality.
Dr. Huld is an opaque, mysterious character who may or may not be helping his clients, especially Josef K. Huld is bedridden but may or may not be ill. He seems to take no action to help his client, K., but relies on his "connections" at court to influence the outcome of the case.
Leni is an attractive woman. She is seductive and flirtatious. She is especially attracted to Dr. Huld's clients. She may be Huld's lover, but may also be involved sexually with his clients. Leni may be using her sexuality to divert Huld's clients' attention away from their cases or to relieve them of their anxiety.
Block is a long-time client of Dr. Huld. He is old and ragged and has been ruined by his case. He is meek, debased, and humiliated by Leni and Huld, who treat him badly and find him pitiful.
Titorelli is a trustee of the court and paints imagined portraits of judges he never sees. He tries to help K. with his case by offering several approaches to his trial—each one paradoxical and pointless.