Wiktionary
n. '''Ayya Vaikundar''' is the incarnation of Ekam(god), in this world as per Akilathirattu Ammanai, the primary scripture of Ayyavazhi religion.
Wikipedia
Ayya Vaikundar (c.1810–c.1851; ), also known as Incarnation of Lord Vishnu, was a 19th-century social reformer and iconoclast who worked for the upliftment of downtrodden people in the Kingdom of Travancore. He is central to the Hindu denomination of Ayyavazhi, as per holy scripture. Akilattirattu Ammanai says that he was Lord Vishnu. In order to attain human form, Vishnu used the body of previous ( Krishna) avatar for the incarnation of Ayya Vaikundar, kept in Parvatha Ucchi Malai (a mythical mountain believed to be in this region) after the completion of the Krishna Avatar. In order to attain natural growth of the human body, Vishnu used the soul of Sampooranathevan a deva also called Mudisoodum Perumal, he was granted moksha (liberation from the cycle of death and birth, synonymous with heaven) before the Ayya Vaikunda Avathar in the sea.
The exact date of birth of Mudisoodum Perumal or Muthukutty is unknown. It is mostly placed in either 1810 or 1809, while others follow the view of Akilam.