There are no doubt certain notions which Buddha shares in common, not only with Kapila, but with every Hindu philosopher. (...) It has been said that Buddha and Kapila were both atheists, and that Buddha borrowed his atheism from Kapila. But atheism is an indefinite term, and may mean very different things. In one sense, every Indian philosopher was an atheist, for they all perceived that the gods of the populace could not claim the attributes that belong to a Supreme Being (Absolute, the source of all that exists or seems to exist, Brahman). (...) Kapila, when accused of atheism, is not accused of denying the existence of an Absolute Being. He is accused of denying the existence of an Ishvara.— Max Muller et al., Studies in Buddhism
Kapila (Sanskrit: कपिल) is a given name of different individuals in ancient and medieval Indian texts, of which the most well-known is the founder of the Samkhya school of Hindu philosophy. Kapila of Samkhya fame is considered a Vedic sage, estimated to have lived in the 6th-century BCE, or the 7th-century BCE.
The name Kapila appears in Jaina texts. For Example, in the 12th century Hemacandra's epic poem on Jain elders, Kapila appears as a Brahmin who converted to Jainism during the Nanda Empire era.
The Śata-piṭaka Series on the Śākhās of the Yajurveda – estimated to have been composed between 1200 and 1000 BCE – mention of a Kapila Śākhā situated in the Āryāvarta, which implies a Yajurveda school was named after Kapila. The term Kapileya, meaning "clans of Kapila", occurs in the Aitareya Brahmana VII.17 but provides no information on the original Kapila. The pariśiṣṭa (addenda) of the Atharvaveda (at XI.III.3.4) mentions Kapila, Āsuri and Pañcaśikha in connection with a libation ritual for whom tarpana is to be offered. In verse 5.2 of Shvetashvatara Upanishad, states Larson, both the terms Samkhya and Kapila appear, with Kapila meaning color as well as a "seer" (Rishi) with the phrase "ṛṣiṃ prasūtaṃ kapilam ... tam agre.."; which when compared to other verses of the Shvetashvatara Upanishad Kapila likely construes to Rudra and Hiranyagarbha. However, Max Muller is of view that Hiranyagarbha, namely Kapila in this context, varies with the tenor of the Upanishad, was distinct and was later used to link Kapila and assign the authorship of Sankya system to Hiranyagarbha in reverence for the philosophical system.