Poopa La Koopa is the grandfather of King Koopa who was briefly mentioned by him in The Super Mario Bros. Super Show! episode "Butch Mario & the Luigi Kid / All Steamed Up".
As Poopa La Koopa is only mentioned in passing by King Koopa, nothing is really known about him, though he seems to be as bad as King Koopa, being said to be a cheater and liar. Poopa La Koopa is Bowser's grandfather, so it could be possible that he is either Bowser's Father's or Mama Koopa's father.