What is Hayat Tahrir al-Sham, rebel group leading Syria offensive?

The Hayat Tahrir al-Sham, (HTS) which launched a counteroffensive against Syrian forces and took over the city of Aleppo, was born out of Jabhat al-Nusra, an Al-Qaeda affiliate, in 2017. The HTS is dedicated to establishing Islamic rule in Syria and expelling Iranian militias. The group has a fighting force of 12,000-15,000 troops according to a report.