Which Caliph compiled the Quran in book form first?

1. Hazrat Umar (R.A)
2. Hazrat Abu Bakr (R.A)
3. Hazrat Usman (R.A)
4. Hazrat Ali (R.A)

Hazrat Abu Bakr (RA) initiated the first official compilation of the Quran into a single manuscript after the Battle of Yamama.