Bethadette, known commonly by the name Big Bertha, is a human adventuress born in Ricklanding, during the 36th year of King Damian's reign. She is the child of a sailor and a barmaid, named Pat and Brenda, and is eight years the elder of her sister, Bessie-Anne.

At age sixteen, Berthadette became enthralled with a passing sailor, an immortal from a distant land. She lost her virginity to him, only to find the next day that the rascal had disappeared, and had only used her for her body. This triggered a deep rage in Berthadette, one that she has never since quenched. She began to comfort eat, and swore to train until the day that she could slay even an immortal being. Through this transformation she became what she is known as today: Big Bertha, six feet in height and six feet in width.

Her weight is impressive, but even more impressive is how skillful an adventurer she remains despite the physical limitations clearly being imposed on her body. Big Bertha was one of the adventurers held captive beneath the Castle of Saints when Messia was overtaken by the Dread Lord, and was freed by Annie Wells. Inside the Messian branch of the Leprechaun's Foot, she battled her younger sister Bessie, for Bertha wished to kill the immortal and Bessie wished to lay with him. However, this timeline was erased by Janus, and Big Bertha remembers none of it.

Big Bertha was later called to Copperdale by Monsieur Federico in order to deal with the Azul crisis, as she was a member of the Champions Guild for dealing with The Mist epidemic, (where she met and worked alongside the mercenary captain John Black.) There, she was compelled by the voice of the sealed Ubaid, given a vision of a bountiful harvest, and so broke into the Museum of Magical Artefacts and freed Ubaid from the sarcophagus he was bound within. Big Bertha witnessed the demon Azulibur open a portal using the museum to summon a demon of great power, only for the demon to itself be captured by Soahc.

The demon crisis resolving itself without Big Bertha's intervention, she then carried on with her adventuring career, eventually ending up in the ogre hills and siding with the ogres of Ogrin. The ogres gave her the name of the White Shaman.

Big Bertha is known to the dwarves as Skinbeard.