Season 1 in Diablo III included several Achievements that were “Season Only”. One group of them was the Paragon Leveling Achievements. As you may have guessed from the name, these Achievements were earned when a player reached a certain Paragon Level on his or her Seasonal character.
One of the goals I set for myself during Season 1 was to hit Paragon 100 on my Seasonal character. In part, this was because I wanted to get all the Seasonal Paragon Leveling Achievements. The bigger reason, though, was because I had never before gotten a character from Level 1 to Level 70 and then gone on to get that same character to Paragon 100.
The Paragon Leveling Achievements were earned when a player hit Paragon Level 10, Paragon Level 25, Paragon Level 50, and Paragon Level 100. There were no further Achievements associated with Paragon leveling in Season 1.