"Whilst we stand, we fight. Whilst we fight, we prevail. Nothing shall stay our wrath."
—Marneus Calgar, Chapter Master of the Ultramarines

Name: William Selark

Chapter: Ultramarines

Equipment: Mark VII Aquila Power Armour
 Two Servo-Arms
 Hesh Pattern Bolter
 Power Axe
 Bolt Pistol

Biography: William was born on Masali into a farming family, his parents were always scared that one day William would be taken to become a Space Marine. The day finally came that, two days after he turned 13, he was taken to begin training. Through the grueling training needing , he finally became a space marine after years of dedication. Throughout his training, he showed proficiency with mechanics. 5 years of serving as a tactical marine had passed before he was admitted into the Adept Mechanicus. William was shipped to mars to be trained as a techmarine. He came back to his Ultramarine brothers a full-fledged techmarine. He spent the next 80 years serving the Ultramarines as a techmarine, until when he was 106, he was seconded to Deathwatch. Ready to slay and cleanse the known galaxy of Xenos scum, he joined Deathwatch and begun his Deathwatch journey.

Notable Achievements: Fought against the Orks in the Assault on Black Reach along side Cato Sicarius, Fought against Hive Ship Behemoth for 10 years. Is renowned for his ability to fix and maintain mechanics.

Physical Description: Short Black hair, X scar on his nose to cheek from fighting a Tyrannid. Looks like a generic space marine with his helmet off. His armor is black, the colour of Deathwatch, save for his helmet which is red to signify that he is a techmarine. His right shoulder is blue and gold with the symbol of the Ultramarines on it, his left should is a black and white with the Skull of the Deathwatch. He also has the symbol of the Adept Mechanicus on his right thigh (on his armor). 

Personality: William is a very loyal marine, during his 5 years before he was admitted into the Adept Mechanicus, he has always been 100% with the Ultramarines. When his loyalties were torn from the Adept Mechanicus and the Ultramarines, he too was torn. But he has learned to adapt from his Techmarine training, and since then have always been quick to adapt. William is also a very open person, able to befriend his fellow marines quickly, but since becoming a Techmarine distrust has fell upon him. The only marines that he has close relations with are his Techmarine brethren. He spends most of his spare time with fixing or creating Mechanics or sometimes the other Techmarines.

I don't think we should include Head Librarians, Head Chaplains, or Masters of the Forge as they wouldn't join Deathwatch due to the fact that they are already heads of the Chapter. It's kinda like the Chapter Master leaving to join Deathwatch but on a smaller scale.