The first occasion was 400 years ago, he was killed as a child by an unknown Fire Dragon, after some time, he was revived by unknown methods by his brother Zeref, who used his body as the ultimae Etherious E. N. D.
Acnologia creates a huge explosion around him, which engulfs Natsu. However, Natsu is unharmed, and he tells Acnologia that there are all kinds of Dragons, some nice and some evil, and also some who are going to defeat Acnologia.
Yes, he dies a long time in the past, prompting Zeref to try to revive him, leading to Natsu becoming END (Etherious Natsu Dragneel), the “God” of Zeref's demons.
How high that strength level rises would vary in different comic books, but most classify Thor in the “Class-100” strength category, which means he can lift well over 100 tons without too much difficulty.
When standing vertically, such as when it functions as a stud, a 2×4 can hold about 1,000 pounds. A 2×4 can hold up to 40 pounds or 300 pounds when laying on its edge without sagging when laying horizontally.