Sparkle Lord (formerly Sparkle Dancer and allegedly Sir Hellacious of Hearts) is an anthropomorphic unicorn from the Radical Lands. In the timeline/universe of Dr. McNinja, he takes the form of a white motorcycle with rainbow trim, as he his true form is too magnificent to exist outside of his home dimension. However, after the Cumberland Mech fight, the world becomes sufficiently radical for him to take a lesser version of his true form. That is to say that he is not at his fully power and is far more magnificent, but at least he isn't a motorcycle. He has been described by King Radical as "Genghis Khan, Adolf Hitler, atomic bombs, and Seabiscuit all in one."
As he tells it, Sparkle Dancer was once an 'ordinary' unicorn who lived in a forest in the Radical Land. This changed when the Kingdom invaded his home, burned down the forest to "build a roller coaster or something" and twisted his shape to conform to what they considered 'cool'. An unknown amount of time later he was knighted "Sir Hellacious of Hearts", making him one of the four Radical Knights alongside Sir SickNasty of Spades, Sir Cowabunga of Clubs and Dame Dudical of Diamonds.
After the death of the previous King Radical, the four knights gathered in a ceremony to name the new King, by tradition chosen by the Radical Land itself. Sparkle Dancer clearly expected to become the new king and was outraged when the land chose Sir Sicknasty instead. Refusing to bow before the new king, he coldly announced that would kill Sir Sicknasty just as he had murdered the previous King Radical.
Sir SickNasty (now King Radical) immediately attacked Sparklelord with such fury and strength that both were sent hurtling through the wall of the tower where the ceremony had taken place. While grappling with the king in mid-air, Sparkle Dancer admitted to tapping the energy of the Radical Land, draining them of energy while becoming stronger himself. This new-found power became evident as he quickly overpowered King Radical and swatted Ron Wizard aside without any apparent effort. Still plummeting to the distant ground, he renounced his old name and proclaimed himself Sparklelord, and gloated that King Radical would be killed by the landing that he himself would walk away from. Fortunately for the new King, he was then caught by a helicopter-head ent (apparently under the command of Dame Dudical), leaving Sparklelord to crash into the ground alone. True to his word, he survived unharmed and immediately declared war on the Radical Lands.
The war itself seems to have been fought between the Radical folk and various magical creatures native to Sparklelord's forest, led by the mad unicorn himself. After many devastating battles, King Radical and Ron Wizard managed to trap Sparklelord and banish him into a time portal. Although this ended the war, the damage done to the Radical Land continued to spread, leaving its inhabitants to face a world increasingly devoid of radical energy. By the time the events of All the King's Dirtbikes and All the King's Men, the corruption has gotten so bad that bad pizza exists.
Chasing King Radical to Cumberland, his form reduced to a motorcycle, he began to possess his riders in the hopes that they would kill his hated enemy for him. Eventually he came across Dr. McNinja (who already disliked King Radical) and attempted to use him to kill King Radical. However, for once Dr. McNinja agreed with King Radical and decides to fling Sparklelord into the Time Portal, trapping him in a time loop.
Sparklelord takes the role of an Anti-Hero alongside the usual Omnicidal Maniac. He is summoned by Dr. McNinja and stops King Radical's plan to get the space Time Portal to Earth in exchange for Dr. McNinja's name. It doesn't work well as King Radical lives and a Ghost Wizard is let loose.