An athlete starts to run positioning his back towards the Sun once after sunrise and once before sunset. He turns left, right and left again. In which direction is he finally running in both scenarios respectively?

Let's trace the path for both scenarios carefully:
Scenario 1: After Sunrise (Sun is in the East)

* Since his back is towards the Sun, he starts running facing West.
* Turn 1 (Left): Facing West $\to$ turns Left $\to$ now faces South.
* Turn 2 (Right): Facing South $\to$ turns Right $\to$ now faces West.
* Turn 3 (Left): Facing West $\to$ turns Left $\to$ finally faces South.

Scenario 2: Before Sunset (Sun is in the West)

* Since his back is towards the Sun, he starts running facing East.
* Turn 1 (Left): Facing East $\to$ turns Left $\to$ now faces North.
* Turn 2 (Right): Facing North $\to$ turns Right $\to$ now faces East.
* Turn 3 (Left): Facing East $\to$ turns Left $\to$ finally faces North.

Therefore, the final directions are South and North respectively.