Thunderstorm

Thunderstorm was a human warrior who wandered the Realms as a nomad mercenary in the mid–14th century DR.

History
Thunderstorm was orphaned when he was a young child and had been on his own since his teenage years.

By 1356 DR, he traveled Faerûn, seeking battles to fight in and what rewards he could win. He survived many battles to become a veteran warrior by the 1360s DR.

In the Year of Blue Fire, 1385 DR, riding his horse, Thunderstorm fled the onrushing effects of the Spellplague, alongside several wild animals.

Skills
His great agility helped him defend himself.

Possessions
He fought with a longsword +3, a shield, and a javelin of lightning, and wore a girdle of stone giant strength. He commonly rode a horse.

Background
This character first appeared in cover art by Keith Parkinson for the Forgotten Realms Campaign Set (nicknamed by fans the Old Gray Box) in 1987, but was unnamed and not mentioned in the books themselves. Reportedly, Parkinson had painted the piece, originally titled "Horseman by the Lake" or "Horseman Near Lake", some time before and reused it for the set. It did not represent any Forgotten Realms character. The "Horseman by the Lake" artwork would go on to be used on other products, such as Spawn of Dragonspear in 1988.

From 1988, Ral Partha Enterprises produced a licensed range of pewter miniatures for D&D, with a Forgotten Realms: Heroes (10-550) collection released in 1989/1990 and bearing the artwork from the Old Gray Box. The cover character was recreated as a miniature (sans horse) and was given the name "Thunderstorm", alongside many then-iconic characters of the Realms. The source of this name is unknown, though the thunderclouds in the background are rather telling.

In 1991, the AD&D Trading Cards produced a card bearing the "Horseman by the Lake" artwork and reused the name Thunderstorm, finally giving him a description and connection to the Realms, if a vague and uninspiring one.

Nevertheless, the character remained obscure to fans. On the former Wizards of the Coast forums in the late 2000s, it was once asked "Who's the dude on a horse on the Old Gray Box?" and Markustay dubbed him "Dood Onahorz", which Lord Karsus revised to "Dûd Onahorz" to sound more Realmsian. The name, and variations of it, stuck and various biographies have since been attached to the fanon character Dûd Onahorz, as discussed here and here. The most notable is George Krashos's story of Daoud yn Ahorz.

A very similar character with minor changes and a different shield but in the same landscape was depicted on page 49 of the Forgotten Realms Campaign Guide presumably in homage to the original artwork. It is presumed they are intended to be the same character.

Despite appearing only in artwork and tie-ins, Thunderstorm, or Dûd Onahorz, is of the most obscure yet iconic characters of the Forgotten Realms, with more background and personality in fans' creations than setting material. He perhaps personifies the generic adventurer of many players.