A.: Ask your colleague directly why he chose to overstep the boundaries of your meeting and jump in the way he did. Tell him that although of course you are glad the business was secured, you do not appreciate the way he handled it. Get him to talk about his motive.
Perhaps he wanted to prove that he can pitch. He may have felt that you were moving too slowly in the beginning. He also may have intended to usurp your position. You won't know until you talk to him about it.
Include in your conversation a recommendation for how you can work together moving forward. Because the deal was secured, you may want to keep him around even if he did annoy you. Suggest that you divide up duties so both of you will have important roles in meetings, since clearly he does not want to be an observer. But it is important to establish ground rules for how you can best work together.