  We demonstrate that the generalization of the relativistic Toda chain (RTC)
is a special reduction of two-dimensional Toda Lattice hierarchy (2DTL). This
reduction implies that the RTC is gauge equivalent to the discrete AKNS
hierarchy and, which is the same, to the two-component Volterra hierarchy while
its forced (semi-infinite) variant is described by the unitary matrix integral.
The integrable properties of the RTC hierarchy are revealed in different
frameworks of: Lax representation, orthogonal polynomial systems, and
$\tau$-function approach. Relativistic Toda molecule hierarchy is also
considered, along with the forced RTC. Some applications to biorthogonal
polynomial systems are discussed.
