Why does Himura Kenshin say ～ござる (~gozaru) at end of every sentence? Why does Himura always end almost every sentence with gozaru in this show? Is this normal for people in that time period?
～ござる is commonly known as a more polite way of ending a sentence, but it's also common in historical dramas because it is a bit archaic-sounding. ANN has an entry on this in their lexicon here. A more detailed analysis of Kenshin's speech patterns can be found here.

EDIT: It was pointed out in chat that there's a closely related question with a really good answer on the Japanese  Stack Exchange.