That’s a tough question. I know it sounds easy enough but upon closer scrutiny, it is not so easy. When Buddhism was introduced into China it brought with it, among other things, a number of sutras on meditation (dhyana) such as the Sutra on perception in the law of practice of meditation, for example. The bottom line, the theory and practice of Zen (dhyana) was known quite early in China.
In early Chinese biographies of eminent Buddhist teachers, one published around 519 A.D. recorded the biographies of 21 Zen teachers. In a later biography published around 645 A.D., 135 Zen teachers biographies are recorded including the immediate disciples of Bodhidharma who is, strangely, not mentioned.
If we want to believe that Bodhidharma was the founder of the Zen lineage 禪宗 it is pretty clear that Zen master Guifeng Zongmi (780–841) played a crucial role in shaping the Song period conception of the Zen lineage as we know it today in many Zen centers. In fact, Zongmi was the first to conceive and name the Chan or Zen lineage 禪宗 in China as an extended clan not Bodhidharma.
Going back much further, this new Zen lineage 禪宗 had it roots in a group of Buddhist monks who studied the Lankavatara Sutra known as the Lanka lineage 楞伽宗 in the Record of Master and Disciple in [the Transmission of] the Lanka 楞伽師資記 which, incidentally, is the subject of J.C. Cleary’s excellent book, Zen Dawn: Early Zen Texts from Tun Huang.
This earlier Lanka lineage 楞伽宗 you could say, morphed into the East Mountain Dharma Gate 東山法門 from where the story of the Sixth Patriarch Huineng was born with his secret transmission from the 5th Patriarch Hongren.
Sound confusing? Well it is not all that confusing. But it does change a few things, one being an unbroken transmission from the Buddha down to present day Zen masters. It never happened the way commonly portrayed in pop Zen circles. If anything that has been transmitted it is a special group of texts which make up the basis of a Zen mythology. Bodhidharma is the founder of the Zen lineage but only in a mythological sense.