Step 1: Collagen exists in at least 28 forms, but for exams the tissue location of the first few types is what matters.
Step 2: A simple memory anchor: Type I is the bone, skin, and tendon collagen, making it the most widespread structural collagen in the body.
Step 3: By contrast, cartilage relies on Type II, reticular networks use Type III, and the basement membrane sheet is Type IV. None of these is the principal skin collagen.
Step 4: Therefore the collagen of skin is Type I.\[\boxed{\text{Type I}}\]