One of GTA 5's smartest design choices is giving each of its three protagonists a distinct special ability, so switching characters genuinely changes how you play. All three share one meter (the yellow bar under the minimap) and one activation input (L3 + R3 on PlayStation, left stick + right stick on Xbox), but what they do is completely different. Here is each one.
Michael: bullet time
Michael's ability is combat slow-motion. Trigger it on foot and time crawls while your aiming stays full speed, letting you line up headshots in the middle of a firefight. It is the most straightforward "win the gunfight" power, and it is why Michael is the default pick for heavy shootouts. It can only be used on foot.
You recharge Michael's meter by driving fast and by scoring special kills: headshots, stealth takedowns and similar.
Franklin: driving focus
Franklin's ability is driving slow-motion. Activate it in any road vehicle and time slows so you can thread traffic, take corners flat-out, and make precise lane changes that would be impossible at full speed. It works in cars and on motorcycles, but not on bicycles, boats or aircraft. Franklin is the driver for a reason; his power makes every chase and getaway easier.
His meter fills by driving stunts: high speed, near-misses, driving into oncoming traffic, and tight escapes.
Trevor: Red Mist
Trevor's ability is pure rage. When Red Mist is active he takes far less damage and deals far more, and crucially he becomes effectively unkillable for the duration, surviving things that would normally be instant death like explosions, big collisions and even getting hit by a train. It turns Trevor into a one-man wrecking crew, which fits him perfectly.
Trevor's meter recharges through violence: killing enemies, taunting, and general mayhem.
Maxing the meter
Each ability lasts longer as you level its stat. At minimum capacity you get about 10 seconds; with the special-ability stat maxed, Michael's and Trevor's last around 30 seconds. You raise the stat simply by using the ability, so lean on it. A practical habit: pop the ability for even a second before it would naturally trigger in a fight or chase, because regular use is what levels the bar.
Which to use when
The rule of thumb is simple: Michael for shootouts, Franklin for driving and chases, Trevor for when you just need to survive and destroy. In free-roam, switching to the right character before a tough encounter is often the difference between a clean run and a reload.
Sources