  A new (in)finite dimensional algebra which is a fundamental dynamical
symmetry of a large class of (continuum or lattice) quantum integrable models
is introduced and studied in details. Finite dimensional representations are
constructed and mutually commuting quantities - which ensure the integrability
of the system - are written in terms of the fundamental generators of the new
algebra. Relation with the deformed Dolan-Grady integrable structure recently
discovered by one of the authors and Terwilliger's tridiagonal algebras is
described. Remarkably, this (in)finite dimensional algebra is a
``$q-$deformed'' analogue of the original Onsager's algebra arising in the
planar Ising model. Consequently, it provides a new and alternative algebraic
framework for studying massive, as well as conformal, quantum integrable
models.
