Trying to draw someone else's character from memory can be an efficient mode of learning for many reasons.
First, the varied nature is simplified into shorthands and generalized forms. This is more evident with Disney characters and Japanese comics. So the form you have to internalize is simplified.
Second, you'll always know, if you've mastered the character's form, by the resemblance of your drawings to the original character. Verification of knowledge is made much easier under this mode of learning.
Third, this is the best part... you'll get to copy the character's different actions, poses, forshortened views, without having to hunt for them in nature.
If the character's a fairly well-constructed one, chances are that when you've mastered drawing the character from memory, you'll have learned something that can be applied to the construction of many other things.