Mighty Morphin Power Rangers
In the Mighty Morphin Power Rangers Series, Skull was very much portrayed as a bully, causing havoc to the Power Rangers in their human forms. Him and Bulk partnered up and caused havoc in the Angel Grove High School. But when it came to facing the monsters they were the first to run away and hide. Later in the series, Bulk and Skull joined the Junior Police Force.
Power Rangers Zeo
In this series we find that Skull and Bulk don't really bully around as much. Him and Bulk are still part of the Junior Police Force, Riding around in a motorcycle with a sides car. We also find that early on in the series that Skull has a real talent for playing the piano, Although very much afraid to tell his best friend Bulk, in fear that Bulk would make fun of him for it, Adam reassures to him that if Bulk was really his friend that he would be proud of his talent. And of course after doing a recital Bulk was very much proud of Skulls talent.
Power Rangers Turbo: Movie
In this movie set right before the Turbo series we see great progression of Bulk and Skull as they are now Police Officers.
Power Rangers Turbo
In this series, Skull and Bulk have lost their badges, and are trying to regain them. When in a turn of events, the two get turned into Chimpanzees for several episodes.
Power Rangers in Space
Bulk and Skull never returned back to the Police Force. Rather instead, the two teamed up with Professor Phenomenus to search for extraterrestrial life. In the series the best came out of the two in the episode where Astronema had a gathering of people around, while asking where the Power Rangers were, no one responded, she was about to attack the civilians when both Bulk and Skull as well as Phenomenus pose as the Power Rangers, to give the Power Ranger time to arrive, and in doing so, the Power Rangers, for the first time ever, broke the code that Zordon came up with all the way back in the Mighty Morphin series, and morphed in front of the civilians, and Proceeded to fight the Pihranatrons and the Quantrons. Bulk and Skull did not like the odds that the Power Rangers were up against, and in that they rallied up the civilians to fight back against Astronema.
Power Rangers Lost Galaxy
Skull was briefly shown in this series, waking up to late to be in time for the boarding of Terra Venture. So he missed out where Bulk and Professor Phenomena made it aboard.
Power Rangers Samurai
Skull was briefly shown in the Samurai series. Throughout the Samurai series his son Spike was sent to live with Bulk. Skull came back to pick Spike up at the end of the series, and it seems that he has had a very successful life. Probably from his skills of being a pianist. This is the last we see from both Bulk and Skull so far.