Turtle is the longtime friend of Master Roshi. He resides at Kame House. Turtle first met Goku while he was lost picking mushrooms. After being returned to Master Roshi, with the help of Goku, Roshi expressed his gratitude by giving Goku the gift of the nimbus cloud. He also gave Bulma the Three Star Dragon Ball.
One of Turtle's, most significant moments in Dragon Ball Z was when he defended Maron from a couple of men who were going to take advantage of her. At this moment we learn that Turtle attains significant fighting ability for that of a Turtle. It can also be assumed that between the time of Raditz arrival and the time of this occurence Turtle must have done some sort of
training. This is due to the fact that we had previously learned the power level of a human being is 5, and that Turtle's power level was previously .001. We would then be able to conclude that Turtle's power level most likely would have increased from .001 to greater than 5.
Turtle makes a brief appearance in Dragon Ball GT, when everyone is saying goodbye to Goku.