In Jainism, Kesi or Kesi Kumār is a significant figure known primarily from the Jain scriptures. He was a learned ascetic and a prominent leader of the Parshvanatha tradition before the time of Lord Mahavira, the 24th Tirthankara.

According to Jain texts, Kesi is most famous for his philosophical debate with Gautama Swami, the chief disciple of Mahavira. This debate is detailed in the "Uttaradhyayana Sutra." During their discussion, Kesi asked Gautama Swami several deep questions about the nature of karma, rebirth, and liberation. Impressed by the answers and the depth of Mahavira's teachings, Kesi and his followers eventually accepted Mahavira's doctrine and became his disciples.

Kesi's story symbolizes the transition and integration of earlier Jain traditions (such as those following Parshvanatha, the 23rd Tirthankara) into the teachings of Mahavira, leading to the unified Jain community known today.