I'm not sure if this has already been covered here but the voices of Greg Universe and Marty, will be doing a reddit Ask Me Anything on r/IAMA! Tom Scharpling and Jon Wurster are both comedians/comedic duo known as Scharpling & Wurster and hosts of The Best Show with Tom Scharpling. Both also guest-voiced Jermaine and Bryce on Adventure Time. Both will be answering questions on August 12 starting at 3 PM ET/12 PM PT so get your questions prepared!
DO NOT, I REPEAT DO NOT, ASK QUESTIONS ON THIS THREAD. Ask them on the Reddit thread (when it gets made) on August 12 at 3pm ET.