There are many representative works of Yan Zhenqing, such as Pagoda Monument, Oriental Painting Praise Monument, Magu Fairy Altar, Guojia Temple Monument, Yan Monument and Temple Monument.
His running script "Ji Ming's Nephew's Manuscript" is a work of grief and indignation, and it is called the second running script in the world. Running scripts include "Contending for Seats" and "Poems by General Pei".
Generally speaking, however, learning Yan-style calligraphy begins with the Pagoda Monument. It's hard to say whether it's the most important thing.