  We study the boundary impurity-induced critical behavior in an integrable
SU(2)-invariant model consisting of an open Heisenberg chain of arbitrary
spin-$S$ (Takhatajian-Babujian model) interacting with an impurity of spin
$\vec{S'}$ located at one of the boundaries. For $S=1/2$ or $S'=1/2$, the
impurity interaction has a very simple form $J\vec{S}_1\cdot\vec{S'}$ which
describes the deformed boundary bond between the impurity $\vec{S'}$ and the
first bulk spin $\vec{S}_1$ with an arbitrary strength $J$. With a weak
coupling $0<J<J_0/[(S+S')^2-1/4]$, the impurity is completely compensated,
undercompensated, and overcompensated for $S=S'$, $S>S'$ and $S<S'$ as in the
usual Kondo problem. While for strong coupling $J\geq J_0/[(S+S')^2-1/4]$, the
impurity spin is split into two ghost spins. Their cooperative effect leads to
a variety of new critical behaviors with different values of $|S'-S|$.
