Complex sentence: Prince Mongkut was a bhikkhu (ordination name: Vajirañāṇo) for 27 years (1824-1851) before becoming the King of Siam (1851-1860); in 1836 he became the first abbot of Wat Bowonniwet.
Split into simpler sentences: Prince Mongkut was a bhikkhu (ordination name: Vajirañāṇo) for 27 years (1824-1851) before becoming the King of Siam (1851-1860). In 1836 he became the first abbot of Wat Bowonniwet.