Jiruses are the most iconic version of Dimension travelers ever known. Jiruses were usually once former humans but when they started taking dimension traveling for granted, they had been deformed. Just green slime with stick-out eyes. Although, the King of all Jiruses had created a way to help them. He gave all of the deformed Jiruses a clear head dome and small, round armor to hold the green slime in place. The king's name was Mastro.
Mastro is the most dangerous Dimension/Universe traveler ever. Mastro is also the first Jirus of all time. He has brought complete destruction to every dimension he has been to. He once brought destruction to our dimension, about 3822812 years ago. He was also born on Earth in our dimension but not anymore, as he lives in every dimension go shows up at.