
Zihark is a playable character introduced in the Fire Emblem game series created by Nintendo, first introduced in Path of Radiance (FE9). Introduced as an recruitable enemy mercenary, he is later discovered to hail from the nation of Daein in the game's sequel, Radiant Dawn (FE10).
He appears in several other games including a bonus DLC character in Awakening (FE13), Heroes (spin-off gacha game), and in the (discontinued) FE trading card series Cipher as of writing.
A compiled set of Zihark images from PoR/RD in one image for drawing/meta reference. Right click and open in new tab for original high resolution.

A close-up high-resolution shot of Zihark in an old promotional artwork. Right click and open in a new tab for highest resolution.

Among other PoR/RD guides that exists, Mediaworks released a pretty substantial gameplay guide for RD. This is Zihark's 2-page profile; he does not have official art in this book. Right click for a larger version to save.

Given the Japanese script is the one that other worldwide translations are based on, it can be useful for fans to comb through the JP script for small character discrepencies. see below for the spreadsheet containing all of Zihark's JP lines across both games.
Rita Suzuki (who draws official Fire Emblem art for many games) once drew work of Zihark in celelbration of the trading card games. You can see it below.

Zihark's name in Japanese is "ツイハーク"; likely derived from Tsui Hark, a Hong Kong filmmaker. A pre-release screenshot from E3 2004 has Zihark's name as ツィハーク Tsihāku instead of the final game's ツイハーク Tsuihāku. In Heroes, his traditional Chinese name is "吉哈克".
A fan checked the translations (in game and the artbook) regarding the scant information given about Zihark's past laguz lover, and confirmed what was implied.
Zihark was briefly shown in several screenshots of a beta version of "Path of Radiance" made for the N64 at E3 2004. Preserved screenshots can be seen below. Development lingered long enough it was decided that game was to be made for the Gamecube one generation later.
Zihark is one of the few recruited units who can defect from the player's side to the enemy side when chosen to speak with the enemy, with Jill being the other.
Zihark has two additional lines in Radiant Dawn's JP-only extended script. A fan translated the whole script (located on the resources page); his two additional lines are listed below.
Zihark (immediately after Tauroneo's "Sothe, you've grown!" line after the battle in the Lost Heir): You even brought Muston and the old gang? And here I was worried you’d found yourselves sent to the camps.