Wolf-Rayet stars are a special type of star that was first discovered by French astronomers, Charles Wolf (1827-1918) and Georges Rayet (1839-1906) who discovered the first in 1867. These stars can be identified by one of their star name starting with WR. For example, Regor is also known as WR11 in addition to Gamma Velorum, HD68273 and HIP39953 and others. WR1 doesn't signify that they were the discovered in that order, the first stars that were discovered have the Id of 134, 135 and 137, all of which are in the constellation of Cygnus. Ref: Wiki
These stars are rare, in fact, according to the Wolf-Rayet Catalog which is frequently updated, there are only about 639 stars of this type out there as at March 2017. This site only has details for the 41 Wolf-Rayet stars that were examined by the Hipparcos space telescope around 1990.
Most Wolf-Rayet are not visible to the naked eye because of their distance to the Earth and because most of their output is in ultraviolet which our eyes can't detect. Ref: Kidzsearch.
Two visible Wolf-Rayet stars are Regor in the constellation of Vela and Theta Muscae in Musca. Both of these stars are in multiple star systems but shouldn't be taken as a rule or an exception. These stars have a very high luminosity. When I say Luminosity I am talking about the amount of visible and non-visible energy that they throw out. These stars are massive compared to our Sun. The luminosity of these stars can be as much as many hundreds of times greater than the luminosity of our own star, the Sun.
No phrase so epitomises Wolf-Rayet stars than that one. When they are created, they are cosmic giants, at least 20x the mass of our Sun. As they are giant stars, they do what giants star are notorious for, they burn through their energy reserves at an alarming rate. A small star such as Proxima Centauri, a tiny red dwarf star will use its fuel supplies at a much lower speed than bigger stars.
Stars become a Wolf-Rayet star when they've used up all or nearly all of their hydrogen. What is happened to all the hydrogen, it has now become helium. The stars outward pressure will overrule the power of gravity and start ejecting out its energy in stellar winds as you can see from the picture below of WR124. After converting helium, it starts to create Lithium, and so on forth up the Periodic Table till it gets to 26, Iron when it can therefore not process any more and explode. Becoming a Wolf-Rayet star is one step in the evolution of the star.
Wolf-Rayet stars have a high metallicity value because a higher percentage of its gas will be non-hydrogen.
A Wolf-Rayet star's life could be over in a matter of millions of years which might seem quite a long time but compare it to the Earth which has about a 10 billion year lifetime for which we are roughly mid-way through. Proxima Centauri is expected to last trillions of years. Ref: Wiki
When they do go out, they'll one almighty explosion. We won't be affected by the explosion in terms of life lost but we could well see it explode in a supernova or even hypernova explosion.
There are three main spectral types of Wolf-Rayet and they are based on the composition of the star and what is the dominant gas in the star. WC (Carbon), WN (Nitrogen) and WO (Oxygen). WO and WC can be classed in the same type Ref: Phys . Each type is further broken down into types that signify their temperature, luminosity and magnitude. The star Regor has a spectral type of WC8 which means it has a temperature of about 60,000 Kelvin, a Radius 4.2x that of the Sun. Its mass is 11x more than our Sun. Its luminosity is 200,000 more than the Sun.
Due to the violent nature of Wolf-Rayet stars, there would be little chance of survival for any planet in orbit. The planet would be scorched to cinders. The Sun is stable compared to Wolf-Rayet stars which has enabled planets to form in orbit round it and provide the facility for life to exist. The first exoplanet to be discovered was found orbiting Lich a.k.a. PSR B1257+12. Lich is a neutron star and people probably bet on pulsars having none but they do.
A Wolf-Rayet is not a special name for a type of star, it is as its name says a galaxy. A Wolf-Rayet is a galaxy with a higher than normal or average star formation. The galaxy will consume and use all its supply of gas and dust up faster than a normal galaxy. An example of a Wolf-Rayet galaxy is irregular galaxy, M82 also known as the Cigar Galaxy.
Because of their sheer size and power, these stars can be spotted in other galaxies. They are not just a phenomena that is limited to the milky way. R136a1 in the nearby Tarantula nebula in the Large Magellanic Cloud is one that we've spotted outside our galaxy. R136a1 is the most massive star so far discovered. It is most massive in terms of mass not diameter.
Below is a picture taken by the Hubble Space Telescope is an example of a Wolf-Rayet star in the constellation of Sagitta. As you can see from the picture, the star is in the middle with its solar winds pushing out.