He finds himself at odds with Anakin Skywalker at one point on the field of battle and he heads the prosecution of Anakin’s padawan Ahsoka when he believes she is guilty of murder.
We first meet Wilhulf Tarkin, chronologically, as a Captain in the Republic Navy in The Clone Wars TV series.
While he’s on the same side as the rest of our heroes, he’s clearly somewhat hostile to our Jedi friends.
It’s also revealed here that Tarkin is already a friend of Chancellor Palpatine, though it’s not clear that he knows any more about him than Anakin Skywalker does at this point.