One word noun for "rule-follower"

I'm looking for a single word noun that would perfectly summarize the stereotypical nerdy uptight virgin student council president.

Basically, a more proper version of the slang word "square": a person who always does what they're supposed to even if it means sacrificing things like fun and happiness and who casts a judgemental gaze on anyone who does otherwise.

I'm trying to describe a certain person, and so far I've got "an OCD, judgemental, paranoid, uptight", but I need a noun to finish it off.

con·form·ist (kn-fôrmst)

n. A person who uncritically or habitually conforms to the customs, rules, or styles of a group.
adj. Marked by conformity or convention: "Underneath the image, teenagers today are surprisingly conformist" (Selina S. Guber).
[emphasis mine]

The RHD entry qualifies the definition with "especially unquestioningly," in place of uncritically. The urbanDictionary sounds more like gingerly :)

alternatively,
fa·nat·ic (f-ntk)

n. A person marked or motivated by an extreme, unreasoning enthusiasm, as for a cause.

Some multi-word answers included because they are idiomatic phrases.

• These have the sense of "snooty, upright, and overly rule-abiding"
  • Goody two-shoes*
  • Goody-goody*
  • Puritan
  • Priss
  • Prude
  • Prig
• These have a sense of "someone who makes things less fun" or "someone who doesn't participate when others are doing something fun"
  • Fuddy-duddy*
  • Killjoy*
  • Stick-in-the-mud*
  • Wet blanket*
  • Spoilsport
  • Party pooper*

* These words are slang

Dogmatist

Noun 1. a stubborn person of arbitrary or arrogant opinions

A common term in the UK is jobsworth, as in "I can't do that [ie break the rules], it's more than my job's worth."

The phrase has contracted to become a one-word noun.

Or how about stickler?