Werner Heisenberg was Bohr’s closest collaborator during the crucial time of consolidation of quantum mechanics (circa 1926).
Heisenberg is (in)famous for proposing to eliminate all but measurable quantities in quantum mechanics. His resulting “theory” is called matrix mechanics.
Heisenberg and Bohr had severe disagreements about the derivation and meaning of the uncertainty relations. See (Camilleri 2007)
Schrödinger and Heisenberg were at each other’s necks in 1926. Bohr suggested that both of them had insights that needed to be taken account of in a final formulation of quantum mechanics.
Heisenberg wrote detailed accounts of his interactions with Bohr, including philosophical discussions (see (Heisenberg 2013). However, the historical accuracy of some of Heisenberg’s accounts (e.g. of their discussions) is somewhat questionable. Heisenberg seems frequently to interpret Bohr’s philosophical statements through the lense of his own evolving philosophy of nature.
Heisenberg was involved in Nazi Germany’s atomic bomb project. Did he try to sabotage it? That’s what he claimed after the war.
(Heelan 2012) (Camilleri 2009)