Page "Mathematical formulation of quantum mechanics" Paragraph 12

Although Schrödinger himself after a year proved the equivalence of his wave-mechanics and Heisenberg's matrix mechanics, the reconciliation of the two approaches and their modern abstraction as motions in Hilbert space is generally attributed to Paul Dirac, who wrote a lucid account in his 1930 classic Principles of Quantum Mechanics.

He is the third, and possibly most important, pillar of that field ( he soon was the only one to have discovered a relativistic generalization of the theory ).

In his above-mentioned account, he introduced the bra-ket notation, together with an abstract formulation in terms of the Hilbert space used in functional analysis ; he showed that Schrödinger's and Heisenberg's approaches were two different representations of the same theory, and found a third, most general one, which represented the dynamics of the system.

His work was particularly fruitful in all kinds of generalizations of the field.