Canaris and Heydrich's wary rivalry

Reinhard Heydrich appears as Canaris's principal rival inside Nazi Germany's intelligence world. Their relationship was more complicated than simple hostility, since Heydrich also seems to have regarded him as something like a friend. One account has Heydrich warning his staff that the "wily old fox" should never be underestimated, though the wording may be apocryphal. The warning captures the rivalry, familiarity, and professional caution between them.