Strikers lead the line. In a 4-3-3 or 4-2-3-1 this is usually a lone number 9; in a 4-4-2 or 3-5-2 the attacking pair splits roles between a holder and a runner.
Archetypes vary wildly: the target man (Haaland), the poacher (Raúl), the all-round number 9 (Lewandowski), and the false 9 (Messi in his Barça prime).
Finishing is the obvious skill, but modern strikers also press the centre-backs, link play with the 10 and hold the ball up for wingers to attack.