Upon his death in 1832, Bentham left instructions for Thomas Southwood Smith to create the auto-icon, with the skeleton and head preserved and stored in the wooden cabinet, and the skeleton padded out with hay and dressed in Bentham's original clothes. Today, the hair and clothes we see are original, as is his skeleton beneath, but the head we see today is a wax model made by a French artist Jacques Talrich. The original head - which was famously kidnapped by King's College students in October 1975 - was mummified and is now kept in special environmental conditions in the Institute of Archaeology. The auto-icon case is usually open from around 8am and closed at 6pm, Monday – Friday, as long as he's not busy attending his occasional UCL board meetings.
For more, see http://www.ucl.ac.uk/museums/jeremy-bentham/