Dongshan was a Chan Buddhist monk born in eastern China during the Tang dynasty, which is to say in the 9th c. CE. He started his Chan studies at a young age, supposedly when at the age of ten he asked a precocious and insightful question about the Heart Sutra. Little is known about his personal life, but he founded a Chan lineage that later gave rise to the Japanese Soto Zen school.

Long seeking it through others,
I was far from reaching it.
Now I go by myself;
I meet it everywhere.
It is just I myself,
And I am not itself.
Understanding this way,
I can be as I am.

Translation Katsuki Sekida