  We realize the first Zeeman slower of an atom in the Main Group III of the
periodic table, otherwise known as the "triel elements". Despite that our atom
of choice (namely indium) does not have a ground state cycling transition
suitable for laser cooling, slowing is achieved by driving the transition
$\lvert 5P_{3/2},F=6 \rangle \rightarrow \lvert 5D_{5/2},F=7 \rangle$, where
the lower-energy state is metastable. Using a slower based on permanent magnets
in a transverse-field configuration, we observe a bright slowed atomic beam at
our design goal velocity of 70 m/s. The techniques presented here can
straightforwardly extend to other triel atoms such as thallium, aluminum, and
gallium. Furthermore, this work opens the possibility of cooling Group III
atoms to ultracold temperatures.
