To get this achievement you must complete all 6 Legend challenges available in the game
Here are each challenge and what you can do to get them.
Legend Badge :
You will get this challenge once all the other ones have been completed
Complete 3 of these Challenges from the highest tiers of Challenge Categories
There are 4 here but you only need to do 3 which are:
10,000 Stat man
Complete any of the 10,000 trick completions Challenges
Load up the 10 mil grind map and you can do the grind 10,000 tricks there
Complete Platinum Score Challenges on 2 Classic Parks
Platinum's are reached when you reach a high enough score on classic parks in a single session most are under 1,000,000 points
Complete 100 Multiplayer Matches
Play the matches like graffiti and trick attack each counts as a "match"
Par for the Course:
Complete a Speed Run under the Par Time for any 3 classic parks with goals
After you beat both tours the speed run option is available in the Ranked and Free Skate section
Speed Run is where you complete all the tasks in the park as fast as you can
The Easiest to complete are Warehouse, School, and The hanger
Warehouse Par Time: 2 minutes
School Par Time: 3 minutes and 15 seconds
The Hanger Par Time: 2 minutes
Complete the Entire collection of challenges for any 3 Pro Skaters, your Create a Skater does not count to this
Rags to Riches:
Complete all the challenges in the Create-a-Skater Collection, doing this will also unlock Officer Dick which is another achievement
Complete every Park and earn all Gold Medals in the Tony Hawk Pro Skater 1 Tour.
Game Modes must be disabled -- For this do all the tasks and get Gold in all competitions in the THPS1 Tour- This is also an achievement
Complete every Park and earn all Gold Medals in the Tony Hawk Pro Skater 2 Tour.
Game modes must be disabled -- For this do all the tasks and get Gold in all competitions in the THPS2 Tour- This is also an achievement