Here is the full list of all 27 Riskers achievements.
Complete all challenges
Complete the game 100%
Complete all achievements
Complete all time attack challenges
Complete the main story missions
Kill Shuba
Kill Thomas
Complete all shizo challenges
Destroy 100 cars
Find all hidden posters
Find the inflatable duck
Complete all side missions
Complete all race challenges
Kill 100 cops
Run over 50 people with a police car
Kill 4 or more people with a single grenade explosion
Unlock brass knuckles
Steal 100 cars
Kill 2 people with a single sniper shot
Smash a window with a chair
Kill 50 people with a baseball bat
Kill 10 enemies with a chair
Kill an armed enemy unarmed
Kill Dino
Kill an enemy while jumping/sliding over an object
Punch and run, have 3 or more people after you
Achieve the fastest car speed