Question about visitors visas/criminal record

My SIL wants to come visit with her boyfriend.  The problem is that he has a criminal record in the US, spent 2 years in jail and was deported back to Canada on his release.  He is and has been, a law abiding citizen in Canada and has no record in the UK.  He holds a Canadian passport. 

Does he need special permission to enter the UK?  Should he have a visa approved prior to entering the country?  They are planning to be here for a few weeks. 

Any advice would be helpful. 

My SIL wants to come visit with her boyfriend.  The problem is that he has a criminal record in the US, spent 2 years in jail and was deported back to Canada on his release.  He is and has been, a law abiding citizen in Canada and has no record in the UK.  He holds a Canadian passport. 

Does he need special permission to enter the UK?  Should he have a visa approved prior to entering the country?  They are planning to be here for a few weeks. 

Any advice would be helpful. 

If he was over 18 when convicted, and there is a comparable conviction in the UK for the same offence, then he needs an entry clearance until the conviction is spent - which is 10 years or 5 years if he was under 18 when convicted.

Thanks Garry.  Very much appreciated!

One more question...  would he need to fill out a VAF1 and provide supporting documents?  And for a sponsor, would that be me - as i'm in the UK?

Also, would an itinerary from a travel agent be sufficient or does he have to have the tickets actually bought and paid for?

One more question...  would he need to fill out a VAF1 and provide supporting documents?  And for a sponsor, would that be me - as i'm in the UK?

Also, would an itinerary from a travel agent be sufficient or does he have to have the tickets actually bought and paid for?

He (or anyone else for that matter) should not purchase tickets in advance of an application - VAF1 or VAF2.  Tickets are not useful as evidence and might result in their loss if the application is delayed or refused. 

A planned itinerary is fine, but even they are not very useful.

To your other q's, yes you are the sponsor. and yes, use a VAF1...