Vader's mask is by far the most iconic element of the character, making the deep breaths feel almost superfluous. Which is why it's surprising that it wasn't a key part of character until well into the screenplay process.
When Ralph McQuarrie realised Vader was travelling from one ship to another in the opening he suggested to Lucas he should wear a breathing mask. It's logical, but it got the director's mind running. Soon he wanted this minor character in his movie more, bumping Vader's role to be a more prevalent threat.
Soon realising just how alluring the respirator was, Lucas eventually decided to have the mask (initially included just for that scene) a permanent robotic suit. Before the mask was added, the plan was to just have whichever actor was cast's face out in the open, with the character potentially sporting some samurai-inspired armour.
Not only would this have made Vader immediately less intimidating, it would have made the subsequent Skywalker twist impossible to pull off, not to mention dating the film more; even today Vader seems futuristic. Neutering the character in its absence, the lack of mask would have given us a less menacing villain and would have in turn weakened the films effect.
The helmet wouldn't have just led to a completely different Vader, but a completely different Star Wars.
Do you love Darth Vader as much as we do? Know any more alternate possibilities of how he could have turned out? Join the discussion in the comment section below.