What's the benefit of having 2 names for the same variable?

I was following this tutorial called Cocos2d Sprite Tutorial, and noticed as below, the variables were first declared in the header file with an extra "_" underscore character at the front.

    CCSprite *_dragon;

    CCAction *_flyAction;

    CCAction *_moveAction;

But then at the @property declaration, the underscore character was removed.

@property (nonatomic, retain) CCSprite *dragon;

@property (nonatomic, retain) CCAction *flyAction;

@property (nonatomic, retain) CCAction *moveAction;

And then in the main ".m" file, both names were used as below with the "=" sign at the "@synthesize".

@synthesize dragon = _dragon;

@synthesize moveAction = _moveAction;

@synthesize flyAction = _flyAction;

And also inside the code both names were referenced as shown below:

        self.dragon = [CCSprite spriteWithSpriteFrame:frame1];

        _dragon.position = ccp( s.width/2-80, s.height/2);

But why? This is the not the first time I saw people doing that, but I don't understand the benefit at all, won't it be very confusing having 2 names for the same variable?

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