Ammar bin Yasir (radiyallahu anhu) is one of the most famous Sahaba and was among the slaves freed by Abu Bakr. He is venerated by Shi'a Muslims as one of the Four Companions, early Muslims who were followers of Ali ibn Abi Talib. He was one of the Muhajirun He is among the List of Sahaba not giving bay'ah to Abu Bakr. Wikipedia
The definitive Wikipedia entry for Ammar Ibn Yasir. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Ammar_ibn_Yasir
