Memento Mori (If Not Today, Tomorry)

There's Juan de Capistrano,
sev'ral Als -- Capone 'n' Capp. 
There's Gabriele Cappellini, 
famous painter chap. 
There's hordes whose handles 
start with 'Cap,' 
tho' few remain afoot. 
Captured, knee-capp'd, then decapitated,
most be now kaput.