Yes, he is. But in the show it's a bit confusing, he could be future Robin, coming back to secretly change little Robin, but that's just my hypothesis. If you want to save the show, go here: http://fightforteentitans.webs.com/
Slade Wilson did not have two kids like the previous person stated. He had three children. His first son, was called Grant, his second son Joseph (or Joey) and his last child was a girl called Rose.
It is never revealed, however the most popular guesses are (in random order)
Slade Wilson (Deathstroke from the comics) Robin's Older Brother (Who may or may not exist) Bruce Wayne/Batman (My...
It was never found out exactly who Slade was in the "Teen Titans" TV series, however, in the "Teen Titans" comic book series, "Deathstroke the Terminator" is a common villain whose real name is Slade...