How did lord Voldemort get his name?

His birth name was Tom Marvolo Riddle.

He hated his name, because his father was a muggle.

However, he made Lord Voldemort out of Tom Marvolo Riddle.

If you rearrange the letters Tom Marvolo Riddle can say

"I am Lord Voldemort."

You see him demonstrate this in HP and the Chamber of Secrets.