How did lucifer become the devil?

Answer 1

Some have equated the verses in Ezekiel 28 and Isaiah 14 as being references to the fall of the 'covering cherub' that the Latin Vulgate called Lucifer or morning star:

Ezekiel 28:14-16New International Version (NIV)

14 You were anointed as a guardian cherub,

for so I ordained you.

You were on the holy mount of God;

you walked among the fiery stones.

15 You were blameless in your ways

from the day you were created

till wickedness was found in you.

16 Through your widespread trade

you were filled with violence,

and you sinned.

So I drove you in disgrace from the mount of God,

and I expelled you, guardian cherub,

from among the fiery stones.