To unlock Officer Dick, you must first create a skater, and then while playing as that skater, complete all 24 challenges under Skater Challenges -> Created Skaters (this will be at the top of the list when you're playing as a created skater).
This will involve you doing the following:
-Getting the sick score in a single combo on every level
-Landing any gap on each level
-Getting all gold medals
-Performing a variety of specific tasks that can be done on any level (usually getting a certain amount of points or doing a certain amount of tricks, sometimes with stipulations such as no grinds, etc.)
-Performing a variety of tasks that are specific to a level (usually getting x amount of points while a certain gap is in your combo, sometimes with stipulations such as no grinds, etc.)
You can get more information by pressing X while highlighting any challenge.
Doing this will also unlock the "Rags to Riches" challenge as part of the Legend collection.