Every Major key has a set of 'native' chords that can be formed by combining notes of the Major scale of that key. A Major scale has 7 Notes/Chords. Each Chord roots on a note of the scale.

The Chords of any Major Key will always have the following Major-Minor Pattern:

I    = Major
ii   = Minor
iii  = Minor
IV  = Major
V   = Major
vi  = Minor
vii = Diminished

Popular Chord Progressions

I - IV - V
I - IV - I - V
I - V - vi - IV
I - ii - IV - V
I - vi - ii - V
I - vi - IV - V