Ubai Ibn Ka'b (radhiyallahu anhu)

He is a man mentioned by the Lord of the Worlds:

Narrated Anas bin Malik:

Allah's Prophet (sallallahu alyhi wasallam) said to Ubai Ibn Ka`b (radhiyallahu anhu), "Allah has ordered me to recite Qur'aan to you." Ubai (radhiyallahu anhu) said, "Did Allah mention me by name to you?" The Prophet (sallallahu alyhi wasallam) said, "Yes." Ubai (radhiyallahu anhu) said, "Have I been mentioned by the Lord of the Worlds?" The Prophet (sallallahu alyhi wasallam) said, "Yes." Then Ubai (radhiyallahu anhu) burst into tears. - Reference: Sahih al-Bukhari 4961

He is one of the greatest scholars of this Ummah:

Ubai Ibn Ka'b said:

Allah's Messenger (sallallahu alyhi wasallam) said: O Abu'l-Mundhir, do you know the verse from the Book of Allah which, according to you, is the greatest? I said: Allah and His Apostle (sallallahu alyhi wasallam) know best. He again said: Abu'l-Mundhir, do you know the verse from the Book of Allah which, according to you, is the greatest? I said: Allah, there is no god but He, the Living, the Eternal. Thereupon he struck me on my breast and said: May knowledge be pleasant for you, O Abu'l-Mundhir! - Reference: Sahih Muslim 810

He is one of the best reciters (Qaari) of the Qur'aan:

Narrated `Abdullah bin `Amr:

I heard the Prophet (sallallahu alyhi wasallam) saying, "Learn the recitation of Qur'aan from four persons: Ibn Mas`ud, Salim, the freed slave of Abu Hudhaifa, Ubai and Mu`adh bin Jabal." - Reference: Sahih al-Bukhari 3806