In Greek, "ego eimi" means, "I AM." When Moses asked God His name, He said, "'I AM who I AM'; and He said, 'Thus you shall say to the sons of Israel, I AM has sent me to you.'" (Ex. 3:14)
Jesus continually called Himself "I AM" (ego eimi) throughout His ministry, which pointed to His deity. This is why the Jehovah's Witness New World Translation mistranslates ego eimi in John 8:58. The correct translation is "before Abraham was born, I AM (ego eimi)." The NWT purposely mistranslates it to "I have been" because they don't want Jehovah's Witnesses to see Jesus' claim of deity.
To be consistent, the New World Translation should have translated "ego eimi" as "I have been" in all other places where it appears. As you can see for the examples below, they translate ego eimi as I AM in all verses except John 8:58.
John 6:48-"I AM (ego eimi) the bread of life."
John 6:51-"I AM (ego eimi) the living bread that came down from heaven…"
John 8:12-"I Am (ego eimi) the light of the world…"
John 8:24-"For if you do not believe that I AM (ego eimi) he ('he' is added by NWT but isn't in the Greek manuscripts), you will die in your sins."
John 10:7-"I AM (ego eimi) the door of the sheep."
John 10:9-"I AM (ego eimi) the door…"
John 10:11-"I AM (ego eimi) the fine shepherd…"
John 10:14-"I AM (ego eimi) the fine shepherd…"
John 11:25-"I AM (ego eimi) the resurrection and the life."
John 14:6-"I AM (ego eimi) the way and the truth and the life."
John 15:1-"I AM (ego eimi) the true vine…"
John 18:5-"He said to them, I AM (ego eimi) he." ('he' is added by NWT but isn't in the Greek manuscripts).
John 8:58-"Before Abraham came into existence, I have been (ego eimi)."