Sakayamuni Buddha is the original and historical founder of Buddhism.
The Three Universal Seals, Four Noble Truths, Eight Fold Paths and Twelve Links of Dependent Origination are the basic foundation to all schools of Buddhism including the Tibetan schools of Vajrayana.
Three-fold training of Precepts, Meditation and Wisdom is universal to all schools.
Organisation of the Buddhist teachings / Dharma into three classications (Sutra, Vinaya and Sastra) is practised among the Buddhist Canons of various countries.
Mind over matter concept. Mind as the principal area of taming and control is fundamental to all schools.