From the Super Mario Wiki
Oogtar is a cave boy resident of Dome City in Dinosaur World. He sometimes causes trouble and appears exclusively in the Super Mario World television series. He wears an animal skin cave man shirt and he has blond hair. His nickname for Yoshi is "Dino Dude". He also acted as a replacement for Toad and is voiced by John Stocker who also voiced as Toad.
Oogtar is perhaps the mischief-maker of the Cave People, as he pulls all sorts of pranks on everyone. Yoshi seems to be his best friend, as evidenced by the fact that Oogtar is usually seen with him.
His first appearance was "Ghosts R Us". He hides out in the Enchanted Forest, with Mario, Luigi, Princess Toadstool, and Yoshi trying to find them. While they're searching for them, Mario, Luigi, and Peach were kidnapped by the Magikoopa, Wizenheimer. Yoshi finds him and they set off to rescue Mario, Luigi, and Peach.
He has appeared in other episodes like "Party Line" and "Rock TV". Three episodes which prominently feature Oogtar are "The Night Before Cave Christmas" and "A Little Learning" and the one above, "Ghosts 'R' Us". The other episodes feature him but not as much. When he appears in other episodes, he's usually for a gag or part of a crowd shot. However in "Rock TV", it's revealed that Oogtar lives with his parents and that he has a sister.
He also speaks with often unfinished, though usually uncomplete sentences. A prime example is "Looky-do, come see!".