Harlek

Harlek is a character in the lore of Dota 2.

Biography
Harlek must've been the creator of the (or at least was involved in its creation), since his possessive name is invoked in this spell. Thus Harlek might've been a mage.

Seeing how the young Invoker (who existed during the ancient days when magery was once at its most potent form because 'twas still primarily a mnemonic art) learned the Sun Strike spell alongside his nine other invocations, Harlek must have existed during this golden age of magic as well and thus this obscure magician must've been an ancient one too.

In Dota: Dragon's Blood
Harlek is nowhere to be seen in the show Dota: Dragon's Blood, but Harlek's does make an appearance, used by none other than the Invoker. This spell, when unused but reserved for immediate casting later on, appeared as a floating orb of fire in front of the Invoker. He brought this orb with him when he confronted Vahdrak, the Father of Chaos, in the dragons' dream.

After a brief conversation between the two, the Invoker prepared to finish off the Thunder by killing Vahdrak. He cast his spell, splitting his flame orb into Quas, Wex, and Exort before they orbited him once and flew into the dark, cloudy sky. A twinkle of light appeared above them where the orbs went up, then an expanding light. Not long after, that light flashed briefly before it shot a beam of light upon Vahdrak, killing him.

Not only is Harlek absent from the show, but the Invoker also doesn't use the right orbs (which is three Exort orbs) for casting Sun Strike. The change might have been done because of the new lore surrounding nature's elements. Since the elements are the Eldwyrms themselves and the whole of the Eldwurms is the Worldwyrm, invoking the power of the Sun (which is also the Worldwyrm) requires the Invoker to combine all the elements. This is just speculation, though.

Inheritance
In his youth, the learned Harlek's  alongside the nine other spells he currently wields, using three Exort orbs to invoke this spell for casting.

Sol Apex
The forgotten Sol Apex Incantation grants its caster access to the Sun's might, which includes a spell akin to Sun Strike. It's unknown if Harlek has any relation to this magic.

Immortality
Harlek must've been a quasi-immortal like the other ancient mages whom Invoker sourced all of his spells from. Assuming that Harlek is still alive like Gallaron, that is.

Magics
Akin to the Invoker, Harlek must have had the power to spells and used  energies for invoking spells. Otherwise, Harlek would not be able to have (also known as Exort Tri-Solar or Harlek's Incantation of Incineration  ) which requires three Exort orbs (or Exort Trionis) to invoke.

This spell channels a devastating ray of energy from the Sun towards the target location, incinerating anyone caught below the sun's concentrated ferocity.

It's implied that the spell has a vast cast range lorewise, so the sunray can be cast beyond the caster's sight, allowing for potential trick shot kills.