  Lev Lipatov was a giant in the field of strong interactions and a dominant
force in high-energy QCD for many decades. His work deeply influenced both how
we think about QCD and how we perform calculations in the theory. Below we
describe the work in two related research directions: the physics of parton
saturation and proton spin at small $x$. Both developments would have been
impossible without Lipatov's groundbreaking work. Saturation physics would not
have happened without the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation. The
recent progress in our theoretical understanding of the proton spin
contribution coming from small-$x$ partons started with the seminal paper by
Kirschner and Lipatov resumming double logarithms of energy in the Reggeon
evolution.
