Rudra and Agni have a close relationship. The identification between Agni and Rudra in the Vedic literature was an important factor in the process of Rudra's gradual development into the later character as Rudra-Shiva. The identification of Agni with Rudra is explicitly noted in the "Nirukta", an important early text on etymology, which says, "Agni is also called Rudra." The interconnections between the two deities are complex, and according to Stella Kramrisch:The fire myth of "Rudra-Śiva" plays on the whole gamut of fire, valuing all its potentialities and phases, from conflagration to illumination.In the "Śatarudrīya", some epithets of Rudra, such as "Sasipañjara" ("Of golden red hue as of flame") and "Tivaṣīmati" ("Flaming bright"), suggest a fusing of the two deities. Agni is said to be a bull, and Lord Shiva possesses a bull as his vehicle, Nandi. The horns of Agni, who is sometimes characterized as a bull, are mentioned. In medieval sculpture, both Agni and the form of Shiva known as Bhairava have flaming hair as a special feature.