In real life, successfully fighting societally recognized enemies gets you all kinds of political opportunity. Look at American Presidents Eisenhower, Grant, Taylor, Jackson, Harrison, and Washington. This is true in nondemocracies too: consider the Duke of Wellington, the Duke of Marlborough, or Sir Francis Drake.

Depends on the situation. A good Samaritan who stopped the kidnapping of the president's daughter because he was in the right place at the right time will get some fame but probably won't be able to leverage that incident into a political career.