Mudaliar also Mudaliyār, Mudali and Moodley in Tamil language literally means a person of first rank in a feudal society in south India. According to Vijaya Ramaswamy in  mudali in the 13th century referred to a title and not specific castes. Due to the process called "sankritization"(every caste takes up the habits and customs of its immediate superior to reach the superior status..) many of Kallars , Maravars and agamudaya thevars became Vellalars . This process started in the Pallav period. . However, in recent times the Mudaliar surname is widely used by people belonging to various castes originally from Tamil Nadu, India and in the Tamil diaspora across the world. Most Mudaliars are Tamil people with Tamil as their mother tongue.
In ancient times, cultivation in South India was spread by force, people would move into virgin land which was used by tribal people for slash and burn agriculture or for hunting and convert it into prime agricultural land. These raids were organized and carried out by chieftains, feudal lords and agricultural landlords called Vellalars. Vellalars are agricultural landlords and inhabitants of the "marutha nilam" (one of the five lands advocated by the Sangam literature). Mudaliar, like Pillai is a title conferred upon prominent Vellalar chieftains and feudal lords by the King depending upon the Tamil Kingdom. More specifically, the Vellalars of Thondaimandalam or the Pallava Kingdom were given the title Mudaliar, while the Vellalars of Pandya and Chola Kingdoms were given
Origin of Vellalars and other castes
During cultural diversification, the Vellalars of TamilNadu can be classified into layers. The first layer consists of Saiva Vellalars (Saiva Vellala Mudaliars and Pillais). They are strict vegetarians, literate and sophisticated like Brahmins but do not perform priestly duties. They were major landlords, feudal lords and powerful like Rajput and Thakurs of Northern India. Saiva Vellalars of the Thondaimandalam became the Thondaimandala Mudaliars. This area includes the present day areas of Chennai, Chingleput, Kanchipuram, Vellore, Cadalore, Arcot, Vadalore, Thrivannamalai, etc. The second layer consists of a number of unique castes, which do not intermarry at all like Pandia Vellalar, (Madurai) Chozhia Vellalar, those who inhabited the areas of Chola (Trichy, Thanjavur, and Pudukottai) and Pandiya mandalams (Madurai, Thuthukudi, Kanyakumari, and Nagerkovil) became the Shoziya Vellar (or "Chola Velar") and Pandiya Vellar respectively.
These communities use Mudaliar, udyar, Pillai titles. The Kaikolar also known as Sengunthar, who are predominantly weavers, cloth merchants and were soldiers under chola empire also use Mudali title. Agamudaiyar, a caste belonging to the Mukkulathor community who generally use Thevar as their surname also use the Mudaliar surname. "Kallarum, Maravarum, Agamudaiyarum mella mella vanthu vellalar anaarkal"- so goes the saying in Tamil.