Stop speaking and observe... Where is this person presenting? Why aren't you presenting there?
I initially typed how you should inform your manager and get colleagues to vouch for you, yet it'll not mean anything. Credit is already given. By complaining, you do nothing productive.
Keep your ideas to yourself, reflect on above two questions and do what's needed. You gotta let the past go. Nothing will come from going after the other person... If they try to get you to speak up more? Then it's a time to enable passwords and leave no document on desk unsecured.
Consider your skills and ideas as "career capital"... Would you leave your credit card out in the open?