The drum machine Doktor Avalanche has been the only constant member of The Sisters of Mercy along with Andrew Eldritch.

The original incarnation of Doktor Avalanche was a BOSS DR-55 ("Doctor Rhythm"); the Doktor was later replaced by a Roland TR-606, soon followed by a TR-808, and, briefly, a TR-909. On one album, First and Last and Always, an Oberheim DMX bore the Doktor name.

With increased financial resources from sale of the album, the Doktor was upgraded to a Yamaha RX5, and subsequently reinforced by Akai S900 and S1000 samplers. An Akai S3200 has been used as studio equipment. Soon after, the first digital Doktor appeared in the form of a set of Compaq portable PCs, which had to be scrapped when it became impossible to maintain them because of a lack of spare parts.

In recent years the "Digital Doktor" has been moved to a custom-built laptop designed by Andrew Eldritch and constructed by an English weapons manufacturing company. For a time there was some division in the band as the whether or not the Doktor should be moved to a Macintosh running Logic or remain as is.

Doktor Avalanche also "runs" the on-line advice column on the Sisters'' website.