The Kālacakratantra is an early eleventh-century esoteric treatise belonging to the class of unexcelled yoga-tantras (anuttara-yoga-tantra). To the best of our knowledge, it was the last anuttara-yoga-tantra to appear in India.
According to the Kālacakra tradition, the extant version of the Kālacakratantra is an abridged version of the larger original tantra, called the Paramādibuddha, that was taught by the Buddha Śākyamuni to Sucandra, the king of Śambhala and an emanation of Vajrapāṇi, in the Dhānyakaṭaka stūpa, a notable center of Mahāyāna in the vicinity of the present-day village of Amarāvatī in Andhra Pradesh. Upon receiving instruction on the Paramādibuddhatantra and returning to Śambhala, King Sucandra wrote it down and propagated it throughout his kingdom. His six successors continued to maintain the inherited tradition, and the eighth king of Śambhala, Mañjuśrī Yaśas, composed the abridged version of the Parāmadibuddhatantra, which is handed down to us as the Sovereign Abridged Kālacakratantra (Laghukālacakratantrarāja). It is traditionally taught that it is composed of 1,030 verses written
in the sradgharā meter. However, various Sanskrit manuscripts and editions of the Laghukālacakratantra contain a somewhat larger number of verses, ranging from 1,037 to 1,047 verses. The term an “abridged tantra” (laghu-tantra) has a specific meaning in Indian Buddhist tantric tradition. Its traditional interpretation is given in Naḍapādas (Nāropā) Sekoddeśaṭīkā, which states that in every yoga, yoginī, and other types of tantras, the concise, general explanations (uddeśa) and specific explanations (nirdeśa) make up a tantric discourse (tantra-saṃgīti), and that discourse, which is an exposition (uddeśana) there, is an entire abridged tantra.
The tradition tells us that Mañjuśrī Yaśas's successor Puṇḍarīka, who was an emanation of Avalokiteśvara, composed a large commentary on the Kālacakratantra, called the Stainless Light (Vimalaprabhā), which became the most authoritative commentary on the Kālacakratantra and served as the basis for all subsequent commentarial literature of that literary corpus. The place of the Vimalaprabhā in the Kālacakra literary corpus is of great importance, for in many instances, without the Vimalaprabhā, it would be practically impossible to understand not only the broader implications of the Kālacakratantra' cryptic verses and often grammatically corrupt sentences but their basic meanings. It has been said that the Kālacakratantra is explicit with regard to the tantric teachings that are often only implied in the other anuttara-yoga-tantras, but this explicitness is actually far more characteristic of the Vimalaprabhā than of the Kālacakratantra itself. (Source: Wallace, Vesna A. The Inner Kālacakratantra: A Buddhist Tantric View of the Individual. New York: Oxford University Press, 2001: pp. 2-3.)