He earned the nickname "Stonewall" at First Manassas (Bull Run to the yankees) during his brigade's defense of Henry Hill. He had other nicknames as well.
Yes, Bull Run is where the nickname came from, but not all agree it was meant as "praise" towards Jackson...
Brig. Gen. Barnard Elliott Bee, Jr. shouted, "There is Jackson standing like a stone wall. Let us determine to die here, and we will conquer. Follow me."
There is some controversy over Bee's statement and intent, which could not be clarified because he was killed almost immediately after speaking and none of his subordinate officers wrote reports of the battle.
Major Burnett Rhett, chief of staff to General Joseph E. Johnston, claimed that Bee was angry at Jackson's failure to come immediately to the relief of Bee's and Bartow's brigades while they were under heavy pressure.
Those who subscribe to this opinion believe that Bee's statement was meant to be pejorative: "Look at Jackson standing there like a damned stone wall!" (Not helping anyone at all, but of course... this impression of what the meaning was didn't stick and dead men tell no tales.[