Hazrat Mahdi (as) is the peacock (adornment)of the Paradise.
(Bihar al-Anwar, Vol 51, p. 105)
Our Prophet (saas) employed an excellent method of telling believers that Hazrat Mahdi (as) will, insha’Allah (by Allah’s will), enjoy a worthy rank in the Hereafter and will be a delightful adornment of Paradise, by saying that Hazrat Mahdi (as) will be the peacock of Paradise. Our Prophet (saas) cites the immaculate beauty of the peacock in order to emphasize Hazrat Mahdi’s (as) intense beauty in Paradise.