Many scholars have written commentaries on the works of Kālidāsa. Among the most studied commentaries are those by Kolāchala Mallinātha Suri, which were written in the 15th century during the reign of the Vijayanagara king, Deva Rāya II. The earliest surviving commentaries appear to be those of the 10th-century Kashmirian scholar Vallabhadeva. Eminent Sanskrit poets like Bāṇabhaṭṭa, Jayadeva and Rajasekhara have lavished praise on Kālidāsa in their tributes. A well-known Sanskrit verse ("Upamā Kālidāsasya...") praises his skill at "upamā", or similes. Anandavardhana, a highly revered critic, considered Kālidāsa to be one of the greatest Sanskrit poets ever. Of the hundreds of pre-modern Sanskrit commentaries on Kālidāsa's works, only a fraction have been contemporarily published. Such commentaries show signs of Kālidāsa's poetry being changed from its original state through centuries of manual copying, and possibly through competing oral traditions which ran alongside the written tradition.