Padmasambhava is regarded as the guru in all the Nyingma's terma (hidden treasure) teaching cycles. For example, when we practice guru yoga, the guru that we visualize is Padmasambhava. Even if we have many root gurus, Padmasambhava can represent all of them. In other words, the nature of Padmasambhava is all of those root gurus. The practice of Padmasambhava contains all the guru yogas.

[Excerpt from Luminous Wisdom Book Series ~ The Guru Yoga Practice of the Seven-Line Prayer to Padmasambhava]