Who are the Alawites, being hunted & killed after fall of Syrian dictator Assad?

Hundreds from Syria's minority Alawite community have been killed in two days of revenge attacks by Sunni Muslim gunmen. Ousted Syrian dictator, President Bashar al-Assad, belonged to the community of Alawites, who make up around 10% of Syria's population. The killings have started following the rise to power of hardline Sunni faction Hayat Tahrir al-Sham, who had deposed Assad.