Randall David Johnson (born September 10, 1963), nicknamed "The Big Unit", is a left-handed Major League Baseball starting pitcher. Over a 21-year career, Johnson has played for 6 different teams, and currently pitches for the San Francisco Giants.

The 6-foot-10 Johnson has been celebrated for having one of the most dominant fastballs in the game. He regularly approached, and occasionally exceeded, 100 miles per hour (160 km/h) during his prime. However, his signature pitch is a hard, biting slider. Johnson has won the Cy Young Award five times, second only to Roger Clemens' seven.

For all active pitchers through the 2008 season, Johnson is first in strikeouts per nine innings pitched (10.67 – which is also first for all starting pitchers in history) and hit batsmen (188 – third all-time), first in strikeouts (4,875 – second all-time), fourth in hits allowed per nine innings pitched (7.24 – 10th all-time), first in shutouts (37 – 57th all-time), third in wins (303 – 22nd all-time), eighth in ERA (3.27), third in wild pitches (104), and seventh in won-lost percentage (.648). His 4,875 strikeouts are also first all-time among left-handed pitchers. In addition, he pitched one of the 18 perfect games in Major League Baseball history.