Who were the next two caliphs after abu bakr?

The next two caliphs after Abu Bakr were Umar ibn al-Khattab and Uthman ibn Affan. Umar, who served as the second caliph from 634 to 644 CE, is known for expanding the Islamic empire significantly and implementing various administrative reforms. Uthman, the third caliph from 644 to 656 CE, is noted for compiling the Quran into a single book and faced challenges that eventually led to his assassination.