Padre Kolbe (Maximilian Maria Kolbe) was a Polish Catholic priest who volunteered to die in place of a prisoner named Franciszek Gajowniczek in Auschwitz concentration camp during WWII. He was one of ten selected to be starved to death as a deterrent warning to the camp inmates after there had been an escape. Ultimately, the Germans wanted to clear the cell in which they were imprisoned and those who had not yet succumbed to starvation (including Kolbe) were given lethal injections.
He was canonized on 10th October 1982 and then regarded as the patron saint of prisoners and drug addicts among others.
As for all Catholic saints, there are lots of versions of medallions and charms produced for sale as amulets. Not easy to say what yours is made of given that it’s enclosed in glass (or lucite or something similar?) but if it were silver it would be marked, so more likely silver-plated. I would assume the encasement was done commercially to protect it as a pocket charm or - if it's heavy enough - as a paperweight. Here’s a similar one produced as a pendant:
Saint Maximilian Kolbe medal, patron of drug addicts and addictions. Browse our large selection of detailed die-cast medals made in the region of Italy that produces the finest quality medals in the world.