Who or what does the Lion of Judah prevail over/overcome in this passage? Revelation 5:5

 

Worthy is the Lamb Revelation 5:12

Who or what does the Lion of Judah prevail over/overcome in this passage?

My bible footnote connects the above passage with Rev 17:14, 

the Lamb overcoming the kings who receive power for one hour with the beast, 

and with Rev 3:21, Christ Jesus saying that He also overcame in the message to the church.

Revelation 5:5

KJV - ⁵ And one of the elders saith unto me, Weep not: behold, the Lion of the tribe of Juda, the Root of David, hath prevailed to open the book, and to loose the seven seals thereof.

Question: Who or what does the Lion of Judah prevail over/overcome in this passage?  Revelation 5:5

See Answer: http://ebible.com/answers/51955?ori=664697