(1) Ali ibn Abi Talib (AS) is one of the most famous sahabah (companions) of Prophet Muhammed (SAW). Ali is actually the Prophet's cousin and he became the husband of the Prophet's daughter, Fatimah (AS). Ali and Fatimah had four children and the most famous were Hassan and Hussain. Ali was blessed with the title Ameer Al Mumineen (Commander of the Faithful) by the Prophet. Ali became the fourth Khalif after the death of the Prophet and Ali is often titled Imam Ali and is loved by all Muslims. Ali is a very popular boy's name.
(2) Ali may also mean high in grandeur but the spelling of this word is usually altered like this 'aliy' or in other ways as the word aliy may be used as a description of God - Al Aliy ul Adheem - The Most High and Most Mighty. In Arabic the word Ali and Aliy are spelt the same.