  We present an overview of the contributions made by Konstantin B. Efetov and
the authors to the field of triplet odd-frequency superconductivity in hybrid
ferromagnet-superconductor structures and the repercussions they had on
experimental and theoretical research. Konstantin B. Efetov passed away in
August 2021. We hope the present short review gives a faithful testimony of an
important part of his scientific legacy.
