When it came to choosing the next Twitter CEO, Costolo said it always came back to Jack. "Jack speaks with the fluency and the moral authority of the inventor of the product."
Inside the walls of Twitter, the feelings are mutual, according to Costolo. "[Jack Dorsey] is inspirational. The team loves working for him."
Costolo is positive on Twitter's future. "It's a resilient company and platform. I'm confident the team will capture the value."
Costolo disclosed he still owns a significant amount of Twitter shares. "The vast majority of my personal and family's net worth is Twitter stock."
—By CNBC Producer Bree Kelly. Follow her on Twitter @Bree_Kelly