Max Steel (Josh or Max McGrath) is the title character in the Max Steel franchise. Depending on the series, he's either a high-schooler with a penchant for extreme sports who is recruited by N-Tek (a secret government agency masquerading as a sports equipment manufacturer) to become a super spy, or he's a high-schooler with alien blood and a robot buddy trying his best to keep his secret identity hidden from his friends.
For the majority of Max's appearances in the original CG-animated series, the Covert Missions video game, as well as the first half of the direct-to-video movies, Christian Campbell voices Max Steel. Due to the timeframe of the original series (right in the heat of the late 1990s/early 2000s XTREME CATCHPHRASE KEWLNESS), Christian's direction seemed to be making Max a more cliche, tough-guy kind of performance. His voice is heroic, but the delivery is a bit clunky.
Matthew Kaminsky filled in for Christian in some of the later episodes of the series. Matthew's Max kind of flips what Christian's was, polishing up the acting and delivery while toning down the ME TOUGH MANLY MAN voice. This could've been due to the series potentially wanting to better differentiate between normal teenager Josh McGrath and N-Tek Super Agent Max Steel.
For the 2009-2012 DTV movies, Mark Hildreth took over the role. At this point in the franchise, Max Steel is now a full-time N-Tek Agent/extreme sports participant. Gone are the days of high-school Josh McGrath, so Mark goes full into the action hero performance.
Andrew Francis lent his vocal talents to Max Steel (now named Max McGrath) in the 2013 reboot. Changing the storyline a little, Max McGrath is now a normal teenager who discovers he's an alien/human hybrid, pumped full of Tachyon Energy. Attempting to balance his life in high-school with defeating superpowered villains, Andrew does a great job of sounding young enough to be a convincing 16 year old (or whatever), but also convincing enough that he wouldn't be some squeaky-voiced teenager struggling for his life.