a Swedish engineer and former professional computer chess programmer. He started chess programming in the 70s, and his first program Dark Horse, written in Fortran and running on a CDC 6600 mainframe computer  and also on a 36-bit one's complement UNIVAC 1100 , played the WCCC 1977 in Toronto, the WCCC 1980 in Linz respectively , and was runner-up at the ECCC 1979.
in chronological order
Princhess was Rathsman's first program for a microcomputer, written in 6502 Assembly to run on a Commodore 64. In 1981, supported by Johan Enroth, Rathsman became professional chess programmer for dedicated chess computers. Soon after Princhess' success as runner-up at the WMCCC 1981 in Travemünde , he started collaboration with Peter-Ingolf Gericke und Klaus Heyne within their company Consumenta, merchandising Conchess chess computers manufactured by Wallharn Electronics, Ireland, with Rathsman's 6502 based Princhess program  . After Consumenta's down and out in 1983, Conchess continued under the aegis of Enroth's company, also marketed by Hegener & Glaser within two models of their Mephisto series  . A Conchess computer competed at the WCCC 1983 in New York .
Princhess became tied World Microcomputer Chess Champion 1984 in Glasgow, where also two Conchess computers competed with the same author involved. In collaboration with co-author Lars Hjörth, Rathsman's next program was Plymate , competing along with Princhess at the WMCCC 1985, and further the WCCC 1986, the WMCCC 1987 and the WMCCC 1988. Y! (Why Not 88 and 89), also with Lars Hjörth as co-author, and Sandro Necchi as book author, competed the WMCCC 1988 and WMCCC 1989, as well the WCCC 1989  . Somewhere in the 90s, Ulf Rathsman retired from computer chess.
- Image cropped from Tidskrift för Schack utges av Sveriges Schackförbund, No. 9, November, 1982, pg. 285, Den "svensktillverkade" schackdatorn Conchess konstruktörer, Ulf Rathsman och Johan Enroth, pdf
- Peter Jennings (1978). Microchess 1.5 Versus Dark Horse. BYTE, Vol. 3, No. 3
- 3rd World Computer Chess Championship - Linz 1980 (ICGA Tournaments)
- Dark Horse' ICGA Tournaments
- László Lindner, A SZÁMÍTÓGÉPES SAKK KÉPEKBEN című melléklete - The pictures of the Beginning of Chess Computers
- Image by László Lindner from László Lindner (1989).Die wiederauferstandene Mikro-Weltmeisterschaft - 8.Mikroschachcomputer - WM 1988 in Almeria. Europa-Rochade, 01/02-1989, pdf hosted by Hein Veldhuis (German)
- Princhess' ICGA Tournaments
- Conchess – Schachcomputer.info Wiki (German)
- Karsten Bauermeister (1998). Die Geschichte der Conchess-Schachcomputer. Computerschach und Spiele, Heft 4, August-September 1998
- Mephisto B&P – Schachcomputer.info Wiki
- Mephisto MM II – Schachcomputer.info Wiki
- Conchess' ICGA Tournaments
- Plymate's ICGA Tournaments
- Y!'s ICGA Tournaments