Answer by taking a quote from the following article:

Todd McFarlane was born on March 16, 1961 in Calgary, Alberta, Canada, to Bob and Sherlee McFarlane. He has two brothers, Curtis and Derek. Bob worked in the printing business, which led him to take work where he could find it, and as a result, during McFarlane's childhood, the family lived in thirty different places from Alberta to California. McFarlane began drawing as a hobby at an early age, and developed an interest in comics, acquiring as many as he could, and learning to draw from them.

McFarlane lost judgments in two lawsuits in the 2000s. The first was a 2002 suit which McFarlane contested with writer Neil Gaiman over the rights to some supporting Spawn characters created by Gaiman in issue No. 9 of the Spawn series and over payment for later works featuring those characters. In 1997 the two signed a deal in which Gaiman would give his share of characters Angela, Medieval Spawn and Cogliostro to McFarlane in exchange for McFarlane's share of British superhero Marvelman (in reality, what McFarlane actually owned were two trademarks for Miracleman logos, not the character, which would become clear only after the lawsuit concluded). This deal was broken by McFarlane, which motivated Gaiman to start the lawsuit. The jury was unanimous in favor of Gaiman. The two were involved in a lengthy dispute over ownership of Miracleman, but no lawsuit has been filed in that dispute. In 2009, Marvel Comics resolved the matter by purchasing the property. The second was a December 2004 suit in which hockey player Tony Twist sued McFarlane because he named a mobster character in Spawn after Twist. The lawsuit was settled out of court for $5 million. As of late 2012, McFarlane was suing a former employee whose name is the same as the alter ego of Spawn, Al Simmons. According to a lawsuit lodged in Arizona federal court, the real Al Simmons published a book called The Art of Being Spawn, in which Simmons purportedly suggests that his own life was the inspiration for the Spawn character. McFarlane's position was that Simmons violated the terms of his employment pact and breached his duty of loyalty. The lawsuit was settled in December 2012 when McFarlane came to an agreement with Simmons. The terms of any settlement were not made public.

What rights was he contesting?
the rights to some supporting Spawn characters created by Gaiman in issue No. 9 of the Spawn series and over payment for later works featuring those characters.