John William "Jo" Callis (born 2 May 1951) is a British musician and songwriter who played guitar with the Edinburgh based punk rock band the Rezillos (under the name Luke Warm) and post-punk band Boots for Dancing, before joining the Human League.

[1] The band played many gigs in Edinburgh and Glasgow, during which Callis wore space suits and other hi-tech costumes.

In late 1978, after the release of the band's only album, the Rezillos split, with Callis forming Shake along with Simon Templar and Angel Paterson.

In the Human League, he played keyboards and lead guitar and contributed as a backing vocalist.

[1] He co-wrote many songs and, following his departure from the band in 1986, returned several times either to play keyboard or to help with songwriting.