Trowser

Trowser is one of the secondary antagonists of The Lost Brother. He is the father of Bowser and undead, taking the form of Dry Bowser. He was defeated by Dragon and Oliver.

Before The Lost Brother
Trowser was the king of the Koopas before Bowser was sworn into the position. Wizenhimer, the then court magikoopa, set a spell on him, so he could not die. Using this newfound power, he tried to take Peach's Castle by force, killing Amadeaus Toadstool III, and Rose Toadstool I. The young Dragon Toadstool sent Trowser to The Minus Zone in retaliation, which was what sparked the never-ending war between the Koopas and the Toads.

In The Minus Zone
Trowser took command of the remaining Koopa army, forcing them to build a portal to help him return home. The portal was completed, but Trowser's mortal body passed away. His skeletal form is all that's left of him. He takes the name of his son, Bowser to disguise himself. After Dragon and Mario's arrival, Trowser found his chance to get revenge on Dragon, but this failed as Dragon and his step-son Oliver defeated him, by shattering his bone leg and causing him to tumble out a window. It is unknown if he will return.

Trivia

 * Dry Bowser may actually be Bowser's father in the canon Mario universe. This is because Dry Bowser has less, and longer hair as well as being larger than the real Bowser; taking New Super Mario Bros. out of consideration.