Well, the Skull was the one who gave him the name Crossbones, because he intended for him to be his sidekick or whatever. I guess they could introduce Crossbones without the Skull being involved, but that would be sort of strange if Cap keeps running into villains with names that reference bones.
Bootleg Batman Begins
: "Bruce found a basement under his villa, in which the equipments turn him into another person: Spiderman. With this mask, Spiderman stroke all criminal activates and criminals everywhere, such as Tougon, the chief of Mafia, Doctor Jackstraw, the abnormal drug trafficker, even a mysterious opponent familiar with him